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.

Example:

Input: 

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

Output: 4

class Solution {
    public int maximalSquare(char[][] matrix) {
        if (matrix.length == 0)
            return 0;
        int m = matrix.length, n = matrix[0].length, max = 0;
        int dp[][] = new int[m][n];
        // dp[i][j] -> length of biggest square possible with lower right corner at i,j
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (i == 0 || j == 0)
                    dp[i][j] = matrix[i][j] == '1' ? 1 : 0;
                else if (matrix[i][j] == '1')
                    dp[i][j] = 1 + Math.min(dp[i - 1][j - 1], Math.min(dp[i - 1][j], dp[i][j - 1]));
                max = Math.max(max, dp[i][j]);
            }
        }
        return max * max;
    }
}