func_code_string: #include <bits/stdc++.h>   using namespace std;   const int maxn = 2000 + 10;   int a[maxn][maxn];   vector<int> G[maxn], R[maxn], topo;   bool v[maxn];   void rdfs(int now) {     v[now] = true;     for (int u : R[now])       if (!v[u]) rdfs(u);     topo.push_back(now);   }   void dfs(int now) {     v[now] = true;     for (int u : G[now])       if (!v[u]) dfs(u);   }   int main() {     ios_base::sync_with_stdio(false);     cin.tie(0);     int n;     cin >> n;     for (int i = 1; i <= n; ++i)       for (int j = 1; j <= n; ++j) {         cin >> a[i][j];         if (a[i][j]) G[i].push_back(j), R[j].push_back(i);       }     for (int i = 1; i <= n; ++i)       if (!v[i]) rdfs(i);     reverse(topo.begin(), topo.end());     memset(v, false, sizeof(v));     dfs(topo[0]);     for (int i = 1; i <= n; ++i)       if (!v[i]) return cout <<  NO  << endl, 0;     cout <<  YES  << endl;     return 0;   }   