func_code_string: #include <bits/stdc++.h>   #pragma comment(linker,  /STACK:65777216 )   using namespace std;   char s[1111][1111];   int n, m;   int best;   int now;   int v[1111][1111];   vector<pair<int, int> > c;   bool u[1111][1111];   void dfs(int x, int y) {     if (u[x][y]) return;     u[x][y] = true;     for (int dx(-1); dx < (2); dx++)       for (int dy(-1); dy < (2); dy++) {         int nx = dx + x;         int ny = dy + y;         if (nx >= 0 && nx < n && ny >= 0 && ny < m)           if (s[nx][ny] ==  0 )             dfs(nx, ny);           else             c.push_back(pair<int, int>(nx, ny));         else           c.push_back(pair<int, int>(-1, -1));       }   }   int startx, starty;   int dfs2(int x, int y, int prevx = -1, int prevy = -1) {     if (x == startx && y == starty && prevx != -1) return 0;     int res = 1;     for (int dx(-1); dx < (2); dx++)       for (int dy(-1); dy < (2); dy++)         if (abs(dx) + abs(dy) == 1) {           int nx = x + dx;           int ny = y + dy;           if (nx >= 0 && nx < n && ny >= 0 && ny < m && v[nx][ny] == v[x][y])             if (nx != prevx || ny != prevy) {               res += dfs2(nx, ny, x, y);               if (prevx == -1) return res;             }         }     return res;   }   int main() {     cin >> n >> m;     for (int i(0); i < (n); i++) scanf(  %s , s[i]);     for (int i(1); i < (n); i++)       for (int j(1); j < (m); j++)         if (s[i][j] ==  1  && s[i][j - 1] ==  1  && s[i - 1][j - 1] ==  1  &&             s[i - 1][j] ==  1 )           best = 4;     for (int i(0); i < (n); i++)       for (int j(0); j < (m); j++)         if (s[i][j] ==  0  && !u[i][j]) {           c.clear();           dfs(i, j);           now++;           bool good = 1;           int num = 0;           for (int k(0); k < (c.size()); k++)             if (c[k].first == -1) {               good = 0;               break;             } else if (v[c[k].first][c[k].second] != now)               v[c[k].first][c[k].second] = now, num++;           for (int k(0); k < (c.size()); k++) {             int num = 0;             for (int dx(-1); dx < (2); dx++)               for (int dy(-1); dy < (2); dy++)                 if (abs(dx) + abs(dy) == 1) {                   int nx = c[k].first + dx;                   int ny = c[k].second + dy;                   if (nx >= 0 && nx < n && ny >= 0 && ny < m && s[nx][ny] ==  1 )                     if (v[nx][ny] == now) num++;                 }             if (num != 2) {               good = 0;               break;             }           }           if (good && num > 4) {             startx = c[0].first;             starty = c[0].second;             if (dfs2(c[0].first, c[0].second) == num) best = max(best, num);           }         }     cout << best << endl;     return 0;   }   