hdu 3836 强连通+缩点：加边构强连通

#include<stdio.h>//求出其所有的强连通分量缩点，选出出度和入度最大的那个就是要求的边
#include<string.h>
#include<stdlib.h>
#define N 51000
struct node {
 int v,next;
}bian[N];
int head[N],yong,n,indegree[N],outdegree[N],visit[N],suo[N],dfn[N],f,low[N],index,stac[N],top;
void addedge(int u,int v) {
bian[yong].v=v;
bian[yong].next=head[u];
head[u]=yong++;
}
void init() {
    memset(head,-1,sizeof(head));
    yong=0;index=0,top=0;f=0;
memset(outdegree,0,sizeof(outdegree));
memset(low,0,sizeof(low));
memset(dfn,0,sizeof(dfn));
memset(indegree,0,sizeof(indegree));
memset(visit,0,sizeof(visit));
memset(stac,0,sizeof(stac));
}
int Min(int a,int b) {
return a>b?b:a;
}
int MAX(int a,int b) {
return a>b?a:b;
}
void tarjan(int u) {
    int v,i;
    dfn[u]=low[u]=++index;
    visit[u]=1;
    stac[++top]=u;
    for(i=head[u];i!=-1;i=bian[i].next) {
        v=bian[i].v;
        if(!dfn[v]) {
            tarjan(v);
            low[u]=Min(low[u],low[v]);
        }
        else
        if(visit[v]==1)
            low[u]=Min(low[u],dfn[v]);
    }
    if(dfn[u]==low[u]) {
        f++;
        int v;
        do{
            v=stac[top--];
            visit[v]=2;
            suo[v]=f;
        }while(v!=u);
    }
}
int main() {
    int m,i,j,fin,fou,v;
    while(scanf("%d%d",&n,&m)!=EOF) {
            if(m==0) {
                printf("%d\n",n);
                continue;
            }
               init();
        while(m--) {
            scanf("%d%d",&i,&j);
            addedge(i,j);
        }
        for(i=1;i<=n;i++)
            if(visit[i]!=2)
        tarjan(i);
            if(f==1) {//判断是否已经是一个联通图
                printf("0\n");
                continue;
            }
       // printf("1\n");
        for(i=1;i<=n;i++)
        for(j=head[i];j!=-1;j=bian[j].next) {
            v=bian[j].v;
          //  printf("%d %d\n",suo[i],suo[v]);
            if(suo[i]!=suo[v]) {
                indegree[suo[v]]++;
            outdegree[suo[i]]++;

            }
        }
        fin=0;fou=0;
        for(i=1;i<=f;i++) {
            if(indegree[i]==0)
               fin++;
               if(outdegree[i]==0)
                fou++;
        }
        printf("%d\n",MAX(fin,fou));
    }
return 0;
}