221. Maximal Square

Problem Link

Description

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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

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Python3

class Solution:
    def maximalSquare(self, matrix: List[List[str]]) -> int:
        rows, cols = len(matrix), len(matrix[0])
        dp = [[0] * cols for _ in range(rows)]
        res = 0
 
        for i in range(rows):
            for j in range(cols):
                if matrix[i][j] == "1":
                    dp[i][j] = 1
                    res = 1
 
        for i in range(1, rows):
            for j in range(1, cols):
                if matrix[i][j] == "1":
                    z = 1 + min(dp[i][j - 1], dp[i - 1][j], dp[i - 1][j - 1])
                    dp[i][j] = z
                    res = max(res, z * z)
                else:
                    dp[i][j] = 0
 
        return res