题目：点击打开链接
思路：强连通分量 中节点数大于1 的个数。
代码：
#include<iostream>
#include<cstdio>
#include<vector>
#include<map>
using namespace std;int n,m;
vector<int> a[10005];
int color[10005]= {0};
int s=0,s1=0;int stack[10005]= {0};
map<int,int> instack;
int top=0;int dfn[10005]= {0},low[10005]= {0};
int num=0;int dfs(int x) {stack[++top]=x;instack[x]=top;dfn[x]=++num;low[x]=num;for(int i=0; i<a[x].size(); i++) {if(color[a[x][i]]==0&&!instack.count(a[x][i])) {low[x]=min(low[x],dfs(a[x][i]));} else if(color[a[x][i]]==0) {low[x]=min(low[x],dfn[a[x][i]]); //}}if(dfn[x]==low[x]) {s++;for(int i=instack[x]; i<=top; i++) {color[stack[i]]=s;}if(instack[x]<top) {s1++;}top=instack[x]-1;}return low[x];}int main() {scanf("%d%d",&n,&m);for(int i=1; i<=m; i++) {int x,y;scanf("%d%d",&x,&y);a[x].push_back(y); }for(int i=1; i<=n; i++) { if(color[i]==0) {dfs(i);}}printf("%d\n",s1);return 0;
}