我看了一下，hack数据好几个输出的是负的，可是代码开了long long，求大佬帮助

#include <bits/stdc++.h>
using namespace std;
#define int long long
const int N = 1e4 + 5;
int n, m, dfn[N], low[N], tim, ans, dp[N];
int cnt, belong[N], sum[N], stk[N], ins[N], top;
bool g[N][N];
vector<int> G[N], G1[N];
void tarjan(int u) {
	dfn[u] = low[u] = ++tim;
	stk[++top] = u, ins[u] = 1;
	for(int v : G[u]) {
		if(!dfn[v]) {
			tarjan(v);
			low[u] = min(low[u], low[v]);
		} else if(ins[v]) {
			low[u] = min(low[u], dfn[v]);
		}
	}
	if(dfn[u] == low[u]) {
		++cnt;
		int tmp;
		do {
			tmp = stk[top--];
			ins[tmp] = 0;
			sum[cnt]++;
			belong[tmp] = cnt;
		} while(tmp != u);
	}
}
signed main() {
	scanf("%lld", &n);
	for(int i = 1; i <= n; i++) {
		for(int j = 1; j <= n; j++) {
			int x;
			scanf("%1lld", &x);
			if(x) G[i].push_back(j);
		}
	}
	for(int i = 1; i <= n; i++) {
		if(!dfn[i]) tarjan(i);
	}
	for(int i = 1; i <= n; i++) {
		for(int j : G[i]) {
			if(belong[i] != belong[j] && !g[belong[j]][belong[i]]) G1[belong[j]].push_back(belong[i]), g[belong[j]][belong[i]] = 1;
		}
	}
	for(int i = 1; i <= cnt; i++) dp[i] = sum[i];
	for(int i = 1; i <= cnt; i++) {
		for(int j : G1[i]) dp[j] += dp[i];
	}
	for(int i = 1; i <= cnt; i++) ans += sum[i] * dp[i];
	printf("%lld", ans);
	return 0;
}