Maximal Square

class Solution {
    public int maximalSquare(char[][] matrix) {
        if(matrix == null ||matrix.length == 0 ) return 0;
        int m = matrix.length;
        int n = matrix[0].length;

        int[][] dp = new int[m+1][n+1];
        int maxLen = 0;
        int prev =0;
        for(int i=1; i <= m ; i++){
            for(int j =1 ; j <=n ; j++){
                if(matrix[i-1][j-1] == '1'){
                    dp[i][j] = Math.min(dp[i-1][j], Math.min(dp[i][j-1], dp[i-1][j-1])) +1;
                    maxLen = Math.max(maxLen, dp[i][j]);
                }else{
                    dp[i][j] = 0; 
                }
            }
        }
        //System.out.println(Arrays.deepToString(dp));
        return maxLen * maxLen;
    }
}