Solution2.java

class Solution {
    private char[][] grid;
    private boolean[][] vis;
    private final int[] dirs = {-1, 0, 1, 0, -1};
    private int m;
    private int n;

    public boolean containsCycle(char[][] grid) {
        this.grid = grid;
        m = grid.length;
        n = grid[0].length;
        vis = new boolean[m][n];
        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;
    }

    private boolean 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;
    }
}