set lambda compare with pair<int, int>

796.cpp

/* Note we compare both first and second element. If we only compare the first, inserting with equal key will fail. 
 * e.g. {4,5} {4,6} will only insert {4,5} although {4,6} is also a valid pair we want here.
 */
auto comp = [](const ii &l, const ii &r) {return l.first==r.first?l.second<r.second:l.first<r.first;};

/*
 * Use decltype to inspects the declared type of an entity or queries the return type of an expression.
 */
set<ii, decltype(comp)> bridges(comp);

int counter=0, critical_links=0;
void ArticulationPoint(int u){
	dfs_num[u]=dfs_low[u]=counter++;	
	for(int j=0;j<(int)adj_list[u].size();++j){
		int v = adj_list[u][j];
		if(dfs_num[v]==kUnvisited){
			dfs_parent[v] = u;
			if(u==dfs_root) root_children++;
			ArticulationPoint(v);
			if(dfs_low[v]>dfs_num[u]){
				critical_links++;
				ii p = u < v ? make_pair(u,v) : make_pair(v,u);
				auto q = bridges.insert(p);
			}
			dfs_low[u] = min(dfs_low[u], dfs_low[v]);
		}
		else if(v != dfs_parent[u]){
			dfs_low[u] = min(dfs_low[u], dfs_num[v]); 
		}
	}
}