Maximal Square

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

For example, given the following matrix:

1 0 1 0 0
1 0 1 1 1
1 1 1 1 1
1 0 0 1 0

Return 4.

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