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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

object Solution {
    def maximalSquare(matrix: Array[Array[Char]]): Int = {
        val m = matrix.length
        if (m == 0) {
            return 0
        }
        val n = matrix(0).length
        if (n == 0) {
            return 0
        }

        val dp = Array.ofDim[Int](m + 1, n + 1)
        var max = 0

        for (i <- 0 until m) {
            for (j <- 0 until n) {
                if (matrix(i)(j) == '1') {
                    val next = 1 + Math.min(dp(i)(j), Math.min(dp(i + 1)(j), dp(i)(j + 1)))
                    if (next > max) {
                        max = next
                    }
                    dp(i + 1)(j + 1) = next
                }
            }
        }

        max * max
    }
}

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