func_code_string: #include <bits/stdc++.h>   using namespace std;   const int maxN(1e3 + 10);   int N, M, P[maxN], A[maxN][maxN], C;   void dfs(const int u) {     C++;     for (int v = 1; v <= N; v++)       if (A[u][v] && !P[v]) {         P[v] = u;         dfs(v);       }   }   int main() {     cin >> N >> M;     if (M != N - 1) {       cout <<  no ;       return 0;     }     for (int i = 0; i < M; i++) {       int u, v;       cin >> u >> v;       A[u][v] = A[v][u] = 1;     }     P[1] = -1;     dfs(1);     cout << (C == N ?  yes  :  no );   }   