void ShGraph<G>::leastCommonAncestor(LCAMap &ancestor)
{
typename VertexSet::const_iterator U, V, W;
typename EdgeSet::const_iterator E;
// First step, identify the "roots" of the DAG (those that have no
// ancestors)
VertexSet roots;
rootSet(roots);
// Find the height of each node by longest path distance from any root
HeightMap heights;
vertexHeight(roots, heights);
// Calculate the transitive closure matrix
TransitiveClosureMap tcm;
transitiveClosure(tcm);
// Identify a candidate least common ancestor (greatest height)
// for each pair of verts
ancestor.clear();
for(U = verts.begin(); U != verts.end(); ++U) {
for(V = verts.begin(); V != verts.end(); ++V) {
int maxHeight = -1;
for(W = verts.begin(); W != verts.end(); ++W) {
// if W is an ancestor of both U and V, check if its the LCA so far
if(tcm(*W, *U) && tcm(*W, *V) && heights[*W] > maxHeight) {
ancestor(*U, *V) = ancestor(*V, *U) = *W;
maxHeight = heights[*W];
}
}
}
}
}
int main()
{
int m;
scanf("%d %d",&n,&m);
for(int i = 0; i < n; i++)
for(int j = 0; j < n; j++)
adj[i][j] = 0;
int u,v;
for(int i = 0; i < m; i++)
{
scanf("%d %d",&u,&v);
adj[u][v] = 1;
}
transitiveClosure();
printReachabilityMatrix();
return 0;
}
