Network---3694poj

#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <algorithm>
#include <vector>
#include <queue>
#include <cmath>
#include <stack>
#include <cstring>
using namespace std;
#define INF 0xfffffff
#define N 101000
int low[N], dfn[N], f[N], bridge[N];
//bridge[i] 是表示i和f[i]之间的路是否是桥；值为1的时候是桥；
vector<vector<int> > G;
int n, Time, m, nbridge;

void Init()
{
    G.clear();
    G.resize(n+1);
    Time = nbridge = 0;
    memset(low, 0, sizeof(low));
    memset(dfn, 0, sizeof(dfn));
    memset(f, 0, sizeof(f));
}

void Tarjan(int u, int father)
{
    f[u] = father;
    dfn[u] = low[u] = ++Time;
    int len = G[u].size(), v;
    for(int i=0; i<len; i++)
    {
        v = G[u][i];
        if(!dfn[v])
        {
            Tarjan(v, u);
            low[u] = min(low[u], low[v]);
            if(low[v] > dfn[u])
            {
                bridge[v]++;
                nbridge++;
            }
        }
        else if(v!=father)//避免找回自己的父节点；
        {
            low[u] = min(low[u], dfn[v]);
        }
    }
}

void LCA(int a, int b)
{
    if( a == b )
        return ;
    if(dfn[a] < dfn[b])
    {
        if(bridge[b]==1)
        {
            bridge[b] = 0;
            nbridge--;
        }
        LCA(a, f[b]);
    }
    else
    {
        if(bridge[a]==1)
        {
            bridge[a] = 0;
            nbridge--;
        }
        LCA(f[a], b);
    }
}

int main()
{
    int t=0, a, b, Q;
    while(scanf("%d %d", &n, &m), n+m)
    {
        Init();
        while(m--)
        {
            scanf("%d %d", &a, &b);
            G[a].push_back(b);
            G[b].push_back(a);
        }
        Tarjan(1,0);
        printf("Case %d:\n", ++t);
        scanf("%d", &Q);
        while(Q--)
        {
            scanf("%d%d", &a,&b);
            LCA(a,b);
            printf("%d\n",nbridge);
        }
        printf("\n");
    }
    return 0;
}