class Solution:    # @param {character[][]} matrix    # @return {integer}    def maximalSquare(self, matrix):        if matrix == []:    return 0        m, n = len(matrix), len(matrix[0])        dp = [[0]*n for i in range(m)]        result = 0        for i in range(m):            for j in range(n):                dp[i][j] = int(matrix[i][j])                if i and j and dp[i][j]:                    dp[i][j] = min(dp[i-1][j-1], dp[i-1][j], dp[i][j-1]) + 1                result = max(result, dp[i][j])        return result*result