LuoguP2002 消息扩散 tarjan求scc

模板，注意有个地方打错好多次了：

for(int j = 0;j < scc[i].size();j++)——是j++不是i++！！！

#include<iostream>
#include<cstdio>
#include<cstring>
#include<vector>
using namespace std;

const int Maxn = 100010; 

int ind[Maxn],dfn[Maxn],low[Maxn],stack[Maxn],ins[Maxn],inscc[Maxn];
vector<int> scc[Maxn],g[Maxn];
int cntscc,cntv,n,m,top;

void tarjan(int x){
    dfn[x] = low[x] = ++cntv;
    ins[x] = 1,stack[++top] = x;
    for(int i = 0;i < g[x].size();i++){
        int u = g[x][i];
        if(!dfn[u])tarjan(u),low[x] = min(low[x],low[u]);
        else if(ins[u])low[x] = min(low[x],dfn[u]);
    }
    if(dfn[x] == low[x]){
        cntscc++; int y = -1;
        while(y != x){
            y = stack[top--];
            ins[y] = 0;
            inscc[y] = cntscc;
            scc[cntscc].push_back(y);
        }
    }
}

int main(){
    cin >> n >> m;
    for(int i = 1;i <= m;i++){
        int x,y;
        cin >> x >> y;
        g[x].push_back(y);
    }
    for(int i = 1;i <= n;i++)if(!dfn[i])tarjan(i);
    for(int i = 1;i <= cntscc;i++){
        for(int j = 0;j < scc[i].size();j++){
            int u = scc[i][j];
            for(int k = 0;k < g[u].size();k++){
                int v = g[u][k];
                if(inscc[v] != i)ind[inscc[v]]++;
            }
        }
    }
    int ans = 0;
    for(int i = 1;i <= cntscc;i++)if(!ind[i])ans++;
    cout << ans;
return 0;
}