s0221_maximal_square

221. Maximal Square

Medium

Given an m x n binary matrix filled with 0's and 1's, find the largest square containing only 1's and return its area.

Example 1:

Input: matrix = [["1","0","1","0","0"],["1","0","1","1","1"],["1","1","1","1","1"],["1","0","0","1","0"]]

Output: 4

Example 2:

Input: matrix = [["0","1"],["1","0"]]

Output: 1

Example 3:

Input: matrix = [["0"]]

Output: 0

Constraints:

• m == matrix.length
• n == matrix[i].length
• 1 <= m, n <= 300
• matrix[i][j] is '0' or '1'.

Solution

from typing import List

class Solution:
    def maximalSquare(self, matrix: List[List[str]]) -> int:
        if not matrix:
            return 0

        m = len(matrix)
        n = len(matrix[0])
        
        if m == 0 or n == 0:
            return 0

        dp = [[0] * (n + 1) for _ in range(m + 1)]
        max_side = 0

        for i in range(m):
            for j in range(n):
                if matrix[i][j] == '1':
                    dp[i + 1][j + 1] = 1 + min(dp[i][j], dp[i + 1][j], dp[i][j + 1])
                    max_side = max(max_side, dp[i + 1][j + 1])

        return max_side * max_side