poj 3352 (雙聯通縮點)

題意：給出一個無向聯通圖，求最少添加幾條邊讓圖是雙聯通圖。

思路：先Tarjan縮點，(求出度數為1的雙聯通分量的個數+1)/2；

#include<stdio.h>#include<string.h>const int N=1100;int dep[N],dfs[N],low[N],ans,idx,head[N],num;struct edge{int st,ed,next;}e[N*100];void addedge(int x,int y){e[num].st=x;e[num].ed=y;e[num].next=head[x];head[x]=num++;e[num].st=y;e[num].ed=x;e[num].next=head[y];head[y]=num++;}void Tarjan(int u,int id){int i,v;dfs[u]=low[u]=++idx;for(i=head[u];i!=-1;i=e[i].next){if(i==(id^1))continue;v=e[i].ed;if(dfs[v]==-1){Tarjan(v,i);low[u]=low[u]>low[v]?low[v]:low[u];}else low[u]=low[u]>dfs[v]?dfs[v]:low[u];}}int main(){int i,n,m,x,y,sum;while(scanf("%d%d",&n,&m)!=-1){memset(head,-1,sizeof(head));num=0;for(i=0;i<m;i++){scanf("%d%d",&x,&y);addedge(x,y);}memset(dfs,-1,sizeof(dfs));ans=idx=0;Tarjan(1,-1);memset(dep,0,sizeof(dep));for(i=0;i<num;i+=2){x=low[e[i].st];y=low[e[i].ed];if(x==y)continue;dep[x]++;dep[y]++;}sum=0;for(i=1;i<=idx;i++){if(dep[i]==1)sum++;}printf("%d\n",(sum+1)/2);}return 0;}