1277. Count Square Submatrices with All Ones

class Solution:
    def countSquares(self, matrix: List[List[int]]) -> int:
        m = len(matrix)
        n= len(matrix[0])
        ans = 0
        dp = [[0] * (n+1) for _ in range(m+1)]
        for i in range(m):
            for j in range(n):
                if matrix[i][j]:
                    dp[i+1][j+1] = min(dp[i+1][j], dp[i][j+1], dp[i][j]) +1
                    ans += dp[i+1][j+1]
        return ans