Reverse the graph
You are given a directed graph with n vertices and m edges. The vertices in the graph are numbered from 1 to n. What is the minimum number of edges you need to reverse in order to have at least one path from vertex 1 to vertex n.
First line contains two integers n and m (1 ≤ n, m ≤ 2 *
106) - the number of vertices and the number of edges. The i-th line of the next m lines contains two integers
yi (1 ≤
yi ≤ n), denoting that the i-th directed edge connects vertices from
Print the minimum number of edges we need to invert. If there is no way of having at least one path from 1 to n, print -1.
7 7 1 2 3 2 3 4 7 4 6 2 5 6 7 5