[Lemon-user] Static Digraph build

[Jean-Bertrand Gauthier]

In the static_digraph.h, one can read from the build function :

     /// The list of the arcs must be given in the range <tt>[begin, 
end)</tt>
     /// specified by STL compatible itartors whose \c value_type must be
     /// <tt>std::pair<int,int></tt>.
     /// Each arc must be specified by a pair of integer indices
     /// from the range <tt>[0..n-1]</tt>. <i>The pairs must be in a
     /// non-decreasing order with respect to their first values.</i>
     /// If the k-th pair in the list is <tt>(i,j)</tt>, then
     /// <tt>arc(k-1)</tt> will connect <tt>node(i)</tt> to 
<tt>node(j)</tt>.


I want to make sure this must be understood such that the arc list cannot be

(0, 1)
(0, 2)
(2, 1)   <- 2 comes before 1
(1, 2)

I'm losing a lot of time to sort my arc vector by first index and I'm 
wondering what I could do save save that cpu time.

thank you