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221. Maximal Square

Difficulty Topics

Description

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

maximal-square.py
class Solution:
    def maximalSquare(self, matrix: List[List[str]]) -> int:
        res = 0
        rows, cols = len(matrix), len(matrix[0])
        dp = [[0] * cols for _ in range(rows)]

        for x in range(rows):
            for y in range(cols):
                if matrix[x][y] == "1":
                    dp[x][y] = 1
                    res = 1

        for x in range(1, rows):
            for y in range(1, cols):
                if matrix[x][y] == "1":
                    z = 1 + min(dp[x][y - 1], dp[x - 1][y - 1], dp[x - 1][y])
                    dp[x][y] = z 
                    res = max(res, z * z)
                else:
                    dp[x][y] = 0

        return res