1 | // -*- C++ -*- |
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2 | /* |
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3 | preflow.h |
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4 | by jacint. |
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5 | Heuristics: |
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6 | 2 phase |
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7 | gap |
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8 | list 'level_list' on the nodes on level i implemented by hand |
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9 | stack 'active' on the active nodes on level i implemented by hand |
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10 | runs heuristic 'highest label' for H1*n relabels |
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11 | runs heuristic 'bound decrease' for H0*n relabels, starts with 'highest label' |
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12 | |
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13 | Parameters H0 and H1 are initialized to 20 and 10. |
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14 | |
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15 | The best preflow I could ever write. |
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16 | |
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17 | The constructor runs the algorithm. |
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18 | |
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19 | Members: |
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20 | |
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21 | T maxFlow() : returns the value of a maximum flow |
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22 | |
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23 | T flowOnEdge(EdgeIt e) : for a fixed maximum flow x it returns x(e) |
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24 | |
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25 | FlowMap Flow() : returns the fixed maximum flow x |
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26 | |
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27 | void minMinCut(CutMap& M) : sets M to the characteristic vector of the |
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28 | minimum min cut. M should be a map of bools initialized to false. |
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29 | |
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30 | void maxMinCut(CutMap& M) : sets M to the characteristic vector of the |
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31 | maximum min cut. M should be a map of bools initialized to false. |
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32 | |
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33 | void minCut(CutMap& M) : sets M to the characteristic vector of |
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34 | a min cut. M should be a map of bools initialized to false. |
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35 | |
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36 | */ |
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37 | |
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38 | #ifndef PREFLOW_H |
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39 | #define PREFLOW_H |
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40 | |
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41 | #define H0 20 |
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42 | #define H1 1 |
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43 | |
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44 | #include <vector> |
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45 | #include <queue> |
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46 | |
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47 | #include <time_measure.h> |
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48 | |
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49 | namespace hugo { |
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50 | |
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51 | template <typename Graph, typename T, |
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52 | typename FlowMap=typename Graph::EdgeMap<T>, |
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53 | typename CapMap=typename Graph::EdgeMap<T> > |
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54 | class preflow { |
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55 | |
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56 | typedef typename Graph::NodeIt NodeIt; |
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57 | typedef typename Graph::EdgeIt EdgeIt; |
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58 | typedef typename Graph::EachNodeIt EachNodeIt; |
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59 | typedef typename Graph::OutEdgeIt OutEdgeIt; |
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60 | typedef typename Graph::InEdgeIt InEdgeIt; |
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61 | |
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62 | Graph& G; |
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63 | NodeIt s; |
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64 | NodeIt t; |
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65 | FlowMap flow; |
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66 | CapMap& capacity; |
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67 | T value; |
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68 | |
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69 | public: |
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70 | double time; |
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71 | preflow(Graph& _G, NodeIt _s, NodeIt _t, CapMap& _capacity ) : |
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72 | G(_G), s(_s), t(_t), flow(_G, 0), capacity(_capacity) |
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73 | { |
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74 | |
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75 | bool phase=0; //phase 0 is the 1st phase, phase 1 is the 2nd |
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76 | int n=G.nodeNum(); |
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77 | int heur0=(int)(H0*n); //time while running 'bound decrease' |
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78 | int heur1=(int)(H1*n); //time while running 'highest label' |
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79 | int heur=heur1; //starting time interval (#of relabels) |
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80 | bool what_heur=1; |
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81 | /* |
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82 | what_heur is 0 in case 'bound decrease' |
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83 | and 1 in case 'highest label' |
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84 | */ |
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85 | bool end=false; |
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86 | /* |
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87 | Needed for 'bound decrease', 'true' |
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88 | means no active nodes are above bound b. |
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89 | */ |
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90 | int relabel=0; |
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91 | int k=n-2; //bound on the highest level under n containing a node |
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92 | int b=k; //bound on the highest level under n of an active node |
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93 | |
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94 | typename Graph::NodeMap<int> level(G,n); |
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95 | typename Graph::NodeMap<T> excess(G); |
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96 | |
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97 | std::vector<NodeIt> active(n); |
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98 | typename Graph::NodeMap<NodeIt> next(G); |
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99 | //Stack of the active nodes in level i < n. |
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100 | //We use it in both phases. |
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101 | |
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102 | typename Graph::NodeMap<NodeIt> left(G); |
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103 | typename Graph::NodeMap<NodeIt> right(G); |
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104 | std::vector<NodeIt> level_list(n); |
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105 | /* |
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106 | List of the nodes in level i<n. |
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107 | */ |
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108 | |
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109 | /*Reverse_bfs from t, to find the starting level.*/ |
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110 | level.set(t,0); |
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111 | std::queue<NodeIt> bfs_queue; |
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112 | bfs_queue.push(t); |
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113 | |
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114 | while (!bfs_queue.empty()) { |
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115 | |
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116 | NodeIt v=bfs_queue.front(); |
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117 | bfs_queue.pop(); |
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118 | int l=level.get(v)+1; |
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119 | |
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120 | for(InEdgeIt e=G.template first<InEdgeIt>(v); e.valid(); ++e) { |
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121 | NodeIt w=G.tail(e); |
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122 | if ( level.get(w) == n && w != s ) { |
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123 | bfs_queue.push(w); |
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124 | NodeIt first=level_list[l]; |
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125 | if ( first != 0 ) left.set(first,w); |
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126 | right.set(w,first); |
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127 | level_list[l]=w; |
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128 | level.set(w, l); |
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129 | } |
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130 | } |
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131 | } |
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132 | |
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133 | level.set(s,n); |
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134 | |
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135 | |
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136 | /* Starting flow. It is everywhere 0 at the moment. */ |
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137 | for(OutEdgeIt e=G.template first<OutEdgeIt>(s); e.valid(); ++e) |
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138 | { |
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139 | T c=capacity.get(e); |
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140 | if ( c == 0 ) continue; |
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141 | NodeIt w=G.head(e); |
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142 | if ( level.get(w) < n ) { |
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143 | if ( excess.get(w) == 0 && w!=t ) { |
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144 | next.set(w,active[level.get(w)]); |
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145 | active[level.get(w)]=w; |
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146 | } |
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147 | flow.set(e, c); |
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148 | excess.set(w, excess.get(w)+c); |
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149 | } |
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150 | } |
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151 | |
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152 | /* |
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153 | End of preprocessing |
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154 | */ |
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155 | |
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156 | |
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157 | |
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158 | /* |
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159 | Push/relabel on the highest level active nodes. |
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160 | */ |
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161 | while ( true ) { |
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162 | |
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163 | if ( b == 0 ) { |
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164 | if ( phase ) break; |
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165 | |
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166 | if ( !what_heur && !end && k > 0 ) { |
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167 | b=k; |
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168 | end=true; |
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169 | } else { |
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170 | phase=1; |
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171 | time=currTime(); |
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172 | level.set(s,0); |
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173 | std::queue<NodeIt> bfs_queue; |
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174 | bfs_queue.push(s); |
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175 | |
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176 | while (!bfs_queue.empty()) { |
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177 | |
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178 | NodeIt v=bfs_queue.front(); |
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179 | bfs_queue.pop(); |
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180 | int l=level.get(v)+1; |
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181 | |
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182 | for(InEdgeIt e=G.template first<InEdgeIt>(v); e.valid(); ++e) { |
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183 | if ( capacity.get(e) == flow.get(e) ) continue; |
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184 | NodeIt u=G.tail(e); |
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185 | if ( level.get(u) >= n ) { |
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186 | bfs_queue.push(u); |
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187 | level.set(u, l); |
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188 | if ( excess.get(u) > 0 ) { |
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189 | next.set(u,active[l]); |
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190 | active[l]=u; |
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191 | } |
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192 | } |
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193 | } |
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194 | |
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195 | for(OutEdgeIt e=G.template first<OutEdgeIt>(v); e.valid(); ++e) { |
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196 | if ( 0 == flow.get(e) ) continue; |
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197 | NodeIt u=G.head(e); |
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198 | if ( level.get(u) >= n ) { |
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199 | bfs_queue.push(u); |
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200 | level.set(u, l); |
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201 | if ( excess.get(u) > 0 ) { |
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202 | next.set(u,active[l]); |
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203 | active[l]=u; |
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204 | } |
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205 | } |
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206 | } |
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207 | } |
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208 | b=n-2; |
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209 | } |
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210 | |
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211 | } |
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212 | |
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213 | |
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214 | if ( active[b] == 0 ) --b; |
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215 | else { |
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216 | end=false; |
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217 | |
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218 | NodeIt w=active[b]; |
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219 | active[b]=next.get(w); |
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220 | int lev=level.get(w); |
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221 | T exc=excess.get(w); |
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222 | int newlevel=n; //bound on the next level of w |
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223 | |
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224 | for(OutEdgeIt e=G.template first<OutEdgeIt>(w); e.valid(); ++e) { |
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225 | |
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226 | if ( flow.get(e) == capacity.get(e) ) continue; |
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227 | NodeIt v=G.head(e); |
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228 | //e=wv |
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229 | |
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230 | if( lev > level.get(v) ) { |
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231 | /*Push is allowed now*/ |
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232 | |
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233 | if ( excess.get(v)==0 && v!=t && v!=s ) { |
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234 | int lev_v=level.get(v); |
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235 | next.set(v,active[lev_v]); |
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236 | active[lev_v]=v; |
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237 | } |
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238 | |
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239 | T cap=capacity.get(e); |
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240 | T flo=flow.get(e); |
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241 | T remcap=cap-flo; |
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242 | |
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243 | if ( remcap >= exc ) { |
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244 | /*A nonsaturating push.*/ |
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245 | |
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246 | flow.set(e, flo+exc); |
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247 | excess.set(v, excess.get(v)+exc); |
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248 | exc=0; |
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249 | break; |
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250 | |
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251 | } else { |
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252 | /*A saturating push.*/ |
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253 | |
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254 | flow.set(e, cap); |
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255 | excess.set(v, excess.get(v)+remcap); |
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256 | exc-=remcap; |
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257 | } |
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258 | } else if ( newlevel > level.get(v) ){ |
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259 | newlevel = level.get(v); |
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260 | } |
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261 | |
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262 | } //for out edges wv |
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263 | |
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264 | |
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265 | if ( exc > 0 ) { |
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266 | for( InEdgeIt e=G.template first<InEdgeIt>(w); e.valid(); ++e) { |
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267 | |
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268 | if( flow.get(e) == 0 ) continue; |
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269 | NodeIt v=G.tail(e); |
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270 | //e=vw |
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271 | |
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272 | if( lev > level.get(v) ) { |
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273 | /*Push is allowed now*/ |
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274 | |
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275 | if ( excess.get(v)==0 && v!=t && v!=s ) { |
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276 | int lev_v=level.get(v); |
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277 | next.set(v,active[lev_v]); |
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278 | active[lev_v]=v; |
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279 | } |
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280 | |
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281 | T flo=flow.get(e); |
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282 | |
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283 | if ( flo >= exc ) { |
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284 | /*A nonsaturating push.*/ |
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285 | |
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286 | flow.set(e, flo-exc); |
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287 | excess.set(v, excess.get(v)+exc); |
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288 | exc=0; |
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289 | break; |
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290 | } else { |
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291 | /*A saturating push.*/ |
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292 | |
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293 | excess.set(v, excess.get(v)+flo); |
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294 | exc-=flo; |
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295 | flow.set(e,0); |
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296 | } |
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297 | } else if ( newlevel > level.get(v) ) { |
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298 | newlevel = level.get(v); |
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299 | } |
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300 | } //for in edges vw |
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301 | |
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302 | } // if w still has excess after the out edge for cycle |
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303 | |
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304 | excess.set(w, exc); |
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305 | |
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306 | /* |
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307 | Relabel |
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308 | */ |
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309 | |
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310 | |
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311 | if ( exc > 0 ) { |
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312 | //now 'lev' is the old level of w |
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313 | |
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314 | if ( phase ) { |
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315 | level.set(w,++newlevel); |
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316 | next.set(w,active[newlevel]); |
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317 | active[newlevel]=w; |
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318 | b=newlevel; |
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319 | } else { |
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320 | //unlacing starts |
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321 | NodeIt right_n=right.get(w); |
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322 | NodeIt left_n=left.get(w); |
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323 | |
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324 | if ( right_n != 0 ) { |
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325 | if ( left_n != 0 ) { |
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326 | right.set(left_n, right_n); |
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327 | left.set(right_n, left_n); |
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328 | } else { |
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329 | level_list[lev]=right_n; |
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330 | left.set(right_n, 0); |
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331 | } |
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332 | } else { |
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333 | if ( left_n != 0 ) { |
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334 | right.set(left_n, 0); |
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335 | } else { |
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336 | level_list[lev]=0; |
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337 | |
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338 | } |
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339 | } |
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340 | //unlacing ends |
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341 | |
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342 | //gapping starts |
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343 | if ( level_list[lev]==0 ) { |
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344 | |
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345 | for (int i=lev; i!=k ; ) { |
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346 | NodeIt v=level_list[++i]; |
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347 | while ( v != 0 ) { |
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348 | level.set(v,n); |
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349 | v=right.get(v); |
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350 | } |
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351 | level_list[i]=0; |
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352 | if ( !what_heur ) active[i]=0; |
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353 | } |
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354 | |
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355 | level.set(w,n); |
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356 | b=lev-1; |
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357 | k=b; |
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358 | //gapping ends |
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359 | } else { |
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360 | |
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361 | if ( newlevel == n ) level.set(w,n); |
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362 | else { |
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363 | level.set(w,++newlevel); |
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364 | next.set(w,active[newlevel]); |
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365 | active[newlevel]=w; |
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366 | if ( what_heur ) b=newlevel; |
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367 | if ( k < newlevel ) ++k; |
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368 | NodeIt first=level_list[newlevel]; |
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369 | if ( first != 0 ) left.set(first,w); |
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370 | right.set(w,first); |
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371 | left.set(w,0); |
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372 | level_list[newlevel]=w; |
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373 | } |
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374 | } |
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375 | |
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376 | |
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377 | ++relabel; |
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378 | if ( relabel >= heur ) { |
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379 | relabel=0; |
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380 | if ( what_heur ) { |
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381 | what_heur=0; |
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382 | heur=heur0; |
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383 | end=false; |
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384 | } else { |
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385 | what_heur=1; |
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386 | heur=heur1; |
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387 | b=k; |
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388 | } |
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389 | } |
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390 | } //phase 0 |
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391 | |
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392 | |
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393 | } // if ( exc > 0 ) |
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394 | |
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395 | |
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396 | } // if stack[b] is nonempty |
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397 | |
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398 | } // while(true) |
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399 | |
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400 | |
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401 | value = excess.get(t); |
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402 | /*Max flow value.*/ |
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403 | |
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404 | } //void run() |
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405 | |
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406 | |
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407 | |
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408 | |
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409 | |
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410 | /* |
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411 | Returns the maximum value of a flow. |
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412 | */ |
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413 | |
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414 | T maxFlow() { |
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415 | return value; |
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416 | } |
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417 | |
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418 | |
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419 | |
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420 | /* |
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421 | For the maximum flow x found by the algorithm, |
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422 | it returns the flow value on edge e, i.e. x(e). |
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423 | */ |
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424 | |
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425 | T flowOnEdge(EdgeIt e) { |
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426 | return flow.get(e); |
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427 | } |
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428 | |
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429 | |
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430 | |
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431 | FlowMap Flow() { |
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432 | return flow; |
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433 | } |
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434 | |
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435 | |
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436 | |
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437 | void Flow(FlowMap& _flow ) { |
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438 | for(EachNodeIt v=G.template first<EachNodeIt>() ; v.valid(); ++v) |
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439 | _flow.set(v,flow.get(v)); |
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440 | } |
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441 | |
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442 | |
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443 | |
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444 | /* |
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445 | Returns the minimum min cut, by a bfs from s in the residual graph. |
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446 | */ |
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447 | |
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448 | template<typename _CutMap> |
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449 | void minMinCut(_CutMap& M) { |
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450 | |
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451 | std::queue<NodeIt> queue; |
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452 | |
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453 | M.set(s,true); |
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454 | queue.push(s); |
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455 | |
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456 | while (!queue.empty()) { |
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457 | NodeIt w=queue.front(); |
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458 | queue.pop(); |
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459 | |
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460 | for(OutEdgeIt e=G.template first<OutEdgeIt>(w) ; e.valid(); ++e) { |
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461 | NodeIt v=G.head(e); |
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462 | if (!M.get(v) && flow.get(e) < capacity.get(e) ) { |
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463 | queue.push(v); |
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464 | M.set(v, true); |
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465 | } |
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466 | } |
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467 | |
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468 | for(InEdgeIt e=G.template first<InEdgeIt>(w) ; e.valid(); ++e) { |
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469 | NodeIt v=G.tail(e); |
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470 | if (!M.get(v) && flow.get(e) > 0 ) { |
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471 | queue.push(v); |
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472 | M.set(v, true); |
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473 | } |
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474 | } |
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475 | } |
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476 | } |
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477 | |
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478 | |
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479 | |
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480 | /* |
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481 | Returns the maximum min cut, by a reverse bfs |
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482 | from t in the residual graph. |
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483 | */ |
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484 | |
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485 | template<typename _CutMap> |
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486 | void maxMinCut(_CutMap& M) { |
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487 | |
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488 | std::queue<NodeIt> queue; |
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489 | |
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490 | M.set(t,true); |
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491 | queue.push(t); |
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492 | |
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493 | while (!queue.empty()) { |
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494 | NodeIt w=queue.front(); |
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495 | queue.pop(); |
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496 | |
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497 | for(InEdgeIt e=G.template first<InEdgeIt>(w) ; e.valid(); ++e) { |
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498 | NodeIt v=G.tail(e); |
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499 | if (!M.get(v) && flow.get(e) < capacity.get(e) ) { |
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500 | queue.push(v); |
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501 | M.set(v, true); |
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502 | } |
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503 | } |
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504 | |
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505 | for(OutEdgeIt e=G.template first<OutEdgeIt>(w) ; e.valid(); ++e) { |
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506 | NodeIt v=G.head(e); |
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507 | if (!M.get(v) && flow.get(e) > 0 ) { |
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508 | queue.push(v); |
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509 | M.set(v, true); |
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510 | } |
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511 | } |
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512 | } |
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513 | |
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514 | for(EachNodeIt v=G.template first<EachNodeIt>() ; v.valid(); ++v) { |
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515 | M.set(v, !M.get(v)); |
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516 | } |
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517 | |
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518 | } |
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519 | |
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520 | |
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521 | |
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522 | template<typename CutMap> |
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523 | void minCut(CutMap& M) { |
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524 | minMinCut(M); |
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525 | } |
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526 | |
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527 | |
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528 | }; |
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529 | |
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530 | } //namespace hugo |
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531 | |
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532 | #endif //PREFLOW_H |
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533 | |
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534 | |
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535 | |
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536 | |
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