leetcode 221. maximal square

https://leetcode.com/problems/maximal-square/

class Solution:
    def maximalSquare(self, matrix: List[List[str]]) -> int:
        m = len(matrix)
        n = len(matrix[0])
        ans = 0
        for i in range(m):
            for j in range(n):
                if i>0 and j>0:
                    vs = map(int, [matrix[i-1][j-1], matrix[i-1][j], matrix[i][j-1]])
                else:
                    vs = [0]
                v = int(matrix[i][j])
                if v == 1:
                    v = max(min(vs) + 1, v)
                    ans = max(v, ans)
                matrix[i][j] = v
        return ans*ans