求桥

c++

来源: http://www.cnblogs.com/cchun/archive/2012/08/18/2645077.html

#include <iostream>
#include <vector>
#include <cstdio>
#include <algorithm>
#include <utility>
#include <cstring>
using namespace std;
typedef struct _node
{
    int v, id, num;
    _node():num(0) {};
}N;
const int MAX = 10005;
vector<N> vec[MAX];
int dfn[MAX], low[MAX], step, id;
int ans[MAX * 10], cnt;
void addEdge(int u, int v)
{
    bool flag = false;
    for(unsigned i = 0; i < vec[u].size(); i++)
    {
        if(vec[u][i].v == v)
        {
            flag = true;
            vec[u][i].num++;
            for(unsigned j = 0; j < vec[v].size(); j++)
            {
                if(vec[v][j].v == u)
                {
                    vec[v][j].num++;
                    break;
                }
            }
            id++;
            break;
        }
    }
    if(flag == false)
    {
        N tmp;
        tmp.v = v, tmp.id = id++;
        tmp.num = 1;
        vec[u].push_back(tmp);
        tmp.v = u;
        vec[v].push_back(tmp);
    }
}
void tarjan(int father, int n)
{
    dfn[n] = low[n] = ++step;
    for(unsigned i = 0; i < vec[n].size(); i++)
    {
        int son = vec[n][i].v;
        if(dfn[son] == -1)
        {
            tarjan(n, son);
            low[n] = min(low[n], low[son]);
        }
        else if(son != father)
            low[n] = min(low[n], dfn[son]);
    }
    if(dfn[n] == low[n])
    {
        int son = n;
        n = father;
        for(unsigned k = 0; k < vec[n].size(); k++)
        {
            if(son == vec[n][k].v)
            {
                if(vec[n][k].num == 1)
                {
                    ans[cnt++] = vec[n][k].id;
                }
                break;
            }
        }
    }
}
void init()
{
    id = 1;
    step = cnt = 0;
    for(int i = 0; i < MAX; i++)
    {
        vec[i].clear();
        dfn[i] = low[i] = -1;
    }
}
int main(void)
{
    int n, m;
    while(std::cin >> n >> m)
    {
        init();
        for(int i = 0; i < m; i++)
        {
            int u, v;
            std::cin >> u >> v;
            addEdge(u, v);
        }
        dfn[1] = low[1] = ++step;
        tarjan(1, 1);
        std::cout << cnt << std::endl;
    }
    return 0;
}