func_code_string: #include <bits/stdc++.h>   using namespace std;   int N;   bool v[2001];   vector<int> G[2001];   int cnt = 0;   int a[2001][2001];   int Dfn[2001], Low[2001];   int Dindex = 0;   int Bcnt;   bool instack[2001];   int Sta[2001];   int top = -1;   void add(int x, int y) { G[x].push_back(y); }   void read() {     scanf( %d , &N);     for (int i = 0; i < N; ++i)       for (int j = 0; j < N; ++j) {         scanf( %d , &a[i][j]);       }     for (int i = 0; i < N; ++i)       for (int j = 0; j < N; ++j)         if (a[i][j] && i != j) add(i, j);   }   void tarjan(int v) {     Dfn[v] = Low[v] = ++Dindex;     instack[v] = 1;     Sta[++top] = v;     for (int i = 0; i < G[v].size(); ++i) {       int w = G[v][i];       if (!Dfn[w]) {         tarjan(w);         Low[v] = min(Low[v], Low[w]);       } else if (instack[w])         Low[v] = min(Low[v], Dfn[w]);     }     int j;     if (Dfn[v] == Low[v]) {       Bcnt++;       do {         j = Sta[top--];         instack[j] = 0;       } while (j != v);     }   }   int main() {     read();     Bcnt = 0;     for (int i = 0; i < N; ++i)       if (!Dfn[i]) tarjan(i);     if (Bcnt > 1)       puts( NO );     else       puts( YES );     return 0;   }   