221. Maximal Square

Given a 2D binary matrix filled with 0’s and 1’s, find the largest square containing only 1’s and return its area.

For example, given the following matrix:

1 0 1 0 01 0 1 1 11 1 1 1 11 0 0 1 0

Return 4.

class Solution {    public int maximalSquare(char[][] matrix) {        if (matrix == null || matrix.length == 0 || matrix[0].length == 0) {            return 0;        }        int m = matrix.length, n = matrix[0].length;        int[][] f = new int[m + 1][n + 1];        int max = 0;        for (int i = 1; i <= m; i++) {            for (int j = 1; j <= n; j++) {                if (matrix[i - 1][j - 1] == '1') {                    f[i][j] = Math.min(f[i - 1][j - 1], Math.min(f[i][j - 1], f[i - 1][j])) + 1;                    max = Math.max(max, f[i][j]);                }            }        }        return max * max;    }}