强连通分量——间谍网络(洛谷_1262)——tarjan求scc

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<vector>
#include<stack>
using namespace std;
inline int read(){
    int t=1,num=0;char c=getchar();
    while(c>‘9‘||c<‘0‘){if(c==‘-‘)t=-1;c=getchar();}
    while(c>=‘0‘&&c<=‘9‘){num=num*10+c-‘0‘;c=getchar();}
    return num*t;
}
const int N=3010;
inline int min(int a,int b){return a<b?a:b;}
vector<int> g[N];stack<int> s;
int pre[N],low[N],biao[N],t=0,cnt=0,d[N];
void dfs(int x){
    pre[x]=low[x]=++t;s.push(x);
    for(int i=0;i<g[x].size();i++){
        int y=g[x][i];
        if(!pre[y]){dfs(y);low[x]=min(low[x],low[y]);}
        else if(!biao[y])low[x]=min(low[x],pre[y]);
    }
    if(low[x]==pre[x]){
        cnt++;int S=-1;
        while(S!=x){
            S=s.top();s.pop();
            biao[S]=cnt;
        }
    }
}
int a[N];
int main()
{
    int n=read(),k=read(),m;
    for(int i=1;i<=k;i++){
        int x=read(),y=read();a[x]=y;
    }
    m=read();
    for(int i=1;i<=m;i++){
        int x=read(),y=read();
        g[x].push_back(y);
    }
    for(int i=1;i<=n;i++)
        if(!pre[i])dfs(i);
    for(int i=1;i<=n;i++)
        for(int j=0;j<g[i].size();j++)
            if(biao[i]!=biao[g[i][j]])
                d[biao[g[i][j]]]++;
    int ans=0,xiao=1e9;
    for(int i=1;i<=cnt;i++){
        if(!d[i]){
            int tmp=1e9,hehe=1e9;
            for(int j=1;j<=n;j++){
                if(a[j]&&biao[j]==i)
                    tmp=min(tmp,a[j]);
                if(biao[j]==i)hehe=min(hehe,j);
            }
            if(tmp==1e9)xiao=min(xiao,hehe);
            else ans+=tmp;
        }
    }
    if(xiao==1e9)printf("YES\n%d\n",ans);
    else printf("NO\n%d\n",xiao);
    return 0;
}