Problem:
Score : 300 points

Problem Statement

You are given an undirected connected graph with N vertices and M edges that does not contain self-loops and double edges.

The i-th edge (1 \leq i \leq M) connects Vertex a_i and Vertex b_i.

An edge whose removal disconnects the graph is called a bridge.

Find the number of the edges that are bridges among the M edges.

Notes

A self-loop is an edge i such that a_i=b_i (1 \leq i \leq M).

Double edges are a pair of edges i,j such that a_i=a_j and b_i=b_j (1 \leq i<j \leq M).

An undirected graph is said to be connected when there exists a path between every pair of vertices.

Constraints

2 \leq N \leq 50

N-1 \leq M \leq min(N(N−1)⁄2,50)

1 \leq a_i<b_i \leq N

The given graph does not contain self-loops and double edges.

The given graph is connected.

Input

Input is given from Standard Input in the following format:

N M
a_1 b_1
a_2 b_2
:
a_M b_M

Output

Print the number of the edges that are bridges among the M edges.

Sample Input 1

7 7
1 3
2 7
3 4
4 5
4 6
5 6
6 7

Sample Output 1

4

The figure below shows the given graph:

The edges shown in red are bridges. There are four of them.

Sample Input 2

3 3
1 2
1 3
2 3

Sample Output 2

0

It is possible that there is no bridge.

Sample Input 3

6 5
1 2
2 3
3 4
4 5
5 6

Sample Output 3

5

It is possible that every edge is a bridge.

Solution in Go (1.6) (judge verdict: Accepted)

package main

import (
  "fmt"
)
var N, M int

var adj[51][]int
var indegree [51]int

func check(from, to int) bool{
  visited := make([]bool, N+1)

  cnt := 0
  for i := 1; i <= N; i++ {
    if visited[i] {
      continue
    }
    cnt += 1
    dfs(i, visited, from, to)
  }
  if cnt > 1 {
    return true
  } else {
    return false
  }
}

func dfs(cur int, visited []bool, from, to int) {
  visited[cur] = true
  for i := 0; i < len(adj[cur]); i++ {
    if cur == from && adj[cur][i] == to {
      continue
    }
    next := adj[cur][i]
    if visited[next] {
      continue
    }
    dfs(next, visited, from, to)
  }
}

func main() {
  fmt.Scanf("%d %d", &N, &M)

  for i := 0; i < M; i++ {
    var a, b int
    fmt.Scanf("%d %d", &a, &b)
    adj[a] = append(adj[a], b)
    adj[b] = append(adj[b], a)
    indegree[a] += 1
    indegree[b] += 1
  }
  ret := 0

  for i := 1; i <= N; i++ {
    for j := 0; j < len(adj[i]); j++ {
      if(check(i, adj[i][j])) {
        ret += 1
//        fmt.Printf("fronm %d to %d\n", i, adj[i][j])
      }
    }
  }
  fmt.Println(ret)
}