Solution2.cpp

class Solution {
public:
    bool containsCycle(vector<vector<char>>& grid) {
        int m = grid.size(), n = grid[0].size();
        vector<vector<bool>> vis(m, vector<bool>(n));
        const vector<int> dirs = {-1, 0, 1, 0, -1};
        function<bool(int, int, int, int)> dfs = [&](int x, int y, int px, int py) {
            vis[x][y] = true;
            for (int k = 0; k < 4; ++k) {
                int nx = x + dirs[k], ny = y + dirs[k + 1];
                if (nx >= 0 && nx < m && ny >= 0 && ny < n) {
                    if (grid[nx][ny] != grid[x][y] || (nx == px && ny == py)) {
                        continue;
                    }
                    if (vis[nx][ny] || dfs(nx, ny, x, y)) {
                        return true;
                    }
                }
            }
            return false;
        };
        for (int i = 0; i < m; ++i) {
            for (int j = 0; j < n; ++j) {
                if (!vis[i][j] && dfs(i, j, -1, -1)) {
                    return true;
                }
            }
        }
        return false;
    }
};