poj 3694 Network（双连通分量）

题目：http://poj.org/problem?id=3694

#include <iostream>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <algorithm>
#include <vector>
using namespace std;
const int MAXN=100010;
int bin[MAXN],n,m;
int low[MAXN],dfn[MAXN],father[MAXN];
int q,cut,index;
vector<int>g[MAXN];

int findx(int x)
{
    return bin[x]==x?x:(bin[x]=findx(bin[x]));
}
int merge(int x,int y)
{
    int fx,fy;
    fx=findx(x);
    fy=findx(y);
    if(fx!=fy)
    {
        bin[fx]=fy;
        return 1;
    }
    else
        return 0;
}

void tarjan(int i,int pre)
{
    int j,k;
    low[i]=dfn[i]=++index;
    for (k=0; k<g[i].size(); k++)
    {
        j = g[i][k];
        if (!dfn[j])
        {
            tarjan(j,i);
            low[i]=min(low[i],low[j]);
            father[j]=i;
            if (low[j] > dfn[i])
                cut++;
            else
                merge(i,j);
        }
        else if (j!=pre)
        {
            low[i]=min(low[i],dfn[j]);
        }
    }
}
void lca(int u,int v)
{
    while (u!=v)
    {
        while (dfn[u]>=dfn[v] && u!=v)
        {
            if (merge(u,father[u]))
                cut--;
            u = father[u];
        }
        while (dfn[v]>=dfn[u]&&u!=v)
        {
            if (merge(v,father[v]))
                cut--;
            v=father[v];
        }
    }
}

int main()
{
    int i,x,y,T=1;
    while(~scanf("%d%d",&n,&m)&&n||m)
    {
        for(i=0; i<=n+1; i++)
        {
            g[i].clear();
            low[i]=dfn[i]=father[i]=0;
            bin[i]=i;
        }
        index=cut=0;

        for(i=0; i<m; i++)
        {
            scanf("%d%d",&x,&y);
            g[x].push_back(y);
            g[y].push_back(x);
        }
        tarjan(1,-1);
        scanf("%d",&q);

        printf("Case %d:
",T++);
        while(q--)
        {
            scanf("%d%d",&x,&y);
            lca(x,y);
            printf("%d
",cut);
        }
        cout<<endl;
    }
    return 0;
}