func_code_string: #include <bits/stdc++.h>   using namespace std;   const int M = 1600;   int dr[] = {-1, 0, 1, 0}, dc[] = {0, 1, 0, -1};   int n, m, pr[M][M], pc[M][M];   char g[M][M], f[M][M];   bool dfs(int r, int c) {     int u = (r % n + n) % n, v = (c % m + m) % m;     if ( #  == g[u][v]) return 0;     if (f[u][v]) return r != pr[u][v] || c != pc[u][v];     f[u][v] = 1, pr[u][v] = r, pc[u][v] = c;     for (int d = 0; d < 4; ++d)       if (dfs(r + dr[d], c + dc[d])) return 1;     return 0;   }   int main(void) {     cin >> n >> m;     for (int i = 0; i < n; ++i) cin >> g[i];     for (int i = 0; i < n; ++i)       for (int j = 0; j < m; ++j)         if ( S  == g[i][j])           cout << (dfs(i + n * 2, j + m * 2) ?  Yes  :  No ) << endl;     return 0;   }   