DFS. Articulation points. Bridges
The undirected graph is given. Find all its bridges.
The first line contains two positive integers n and m (n ≤ 20000, m ≤ 200000) - the number of vertices and edges in a graph respectively. Each of the next m lines contains the description of one edge. The edge number i is described with two positive integers
ei (1 ≤
ei ≤ n) - the numbers of the vertices it connects.
Print in the first line the number b of bridges in a given graph. Print on the next line b integers - the edge numbers that are bridges, in increasing order. The edges are numbered from one in the order they are given at the input.
6 7 1 2 2 3 3 4 1 3 4 5 4 6 5 6