221. 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(object):
    def maximalSquare(self, matrix):
        """
        :type matrix: List[List[str]]
        :rtype: int
        """
        if matrix == []:
            return 0
        m = len(matrix)
        n = len(matrix[0])
        
        maxedge = 0
        
        for i in range(m):
            for j in range(n):
                matrix[i][j] = int(matrix[i][j])
                if matrix[i][j] and i and j:
                    matrix[i][j] = min(matrix[i][j-1], matrix[i-1][j], matrix[i-1][j-1]) + 1
                maxedge = max(maxedge, matrix[i][j])
                
        return maxedge **2