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 == null || matrix.length == 0 || matrix[0].length == 0) return 0;
        int row = matrix.length;
        int col = matrix[0].length;
        int[][] dp = new int[row][col];
        int max = 0;
        for(int i = 0; i < row; i++) {
            if(matrix[i][0] == '1') dp[i][0] = 1;
            else dp[i][0] = 0;
            max = Math.max(max, dp[i][0]);
        }
        for(int j = 0; j < col; j++) {
            if(matrix[0][j] == '1') dp[0][j] = 1;
            else dp[0][j] = 0;
            max = Math.max(max, dp[0][j]);
        }


        for(int i = 1; i < row; i++) {
            for(int j = 1; j < col; j++) {
                if(matrix[i][j] == '0') dp[i][j] = 0;
                else {
                    dp[i][j] = Math.min(dp[i-1][j-1], Math.min(dp[i-1][j], dp[i][j-1])) + 1;
                    max = Math.max(max, dp[i][j]);
                }
            }
        }
        return max * max;
    }
}



class Solution {
    public int maximalSquare(char[][] matrix) {
        if(matrix == null || matrix.length == 0 || matrix[0].length == 0) return 0;
        int row = matrix.length;
        int col = matrix[0].length;
        int[][] dp = new int[row+1][col+1];
        int max = 0;        

        for(int i = 1; i <= row; i++) {
            for(int j = 1; j <= col; j++) {
                if(matrix[i-1][j-1] == '0') dp[i][j] = 0;
                else {
                    dp[i][j] = Math.min(dp[i-1][j-1], Math.min(dp[i-1][j], dp[i][j-1])) + 1;
                    max = Math.max(max, dp[i][j]);
                }
            }
        }
        return max * max;
    }
}