LeetCode in Kotlin

931. Minimum Falling Path Sum

Medium

Given an n x n array of integers matrix, return the minimum sum of any falling path through matrix.

A falling path starts at any element in the first row and chooses the element in the next row that is either directly below or diagonally left/right. Specifically, the next element from position (row, col) will be (row + 1, col - 1), (row + 1, col), or (row + 1, col + 1).

Example 1:

Input: matrix = [[2,1,3],[6,5,4],[7,8,9]]

Output: 13

Explanation: There are two falling paths with a minimum sum as shown.

Example 2:

Input: matrix = [[-19,57],[-40,-5]]

Output: -59

Explanation: The falling path with a minimum sum is shown.

Constraints:

• n == matrix.length == matrix[i].length
• 1 <= n <= 100
• -100 <= matrix[i][j] <= 100

Solution

class Solution {
    fun minFallingPathSum(matrix: Array<IntArray>): Int {
        val l = matrix[0].size
        var arr = matrix[0]
        for (i in 1 until matrix.size) {
            val cur = IntArray(l)
            for (j in 0 until l) {
                var left = Int.MAX_VALUE
                var right = Int.MAX_VALUE
                val curCell = arr[j]
                if (j > 0) {
                    left = arr[j - 1]
                }
                if (j < l - 1) {
                    right = arr[j + 1]
                }
                cur[j] = matrix[i][j] + left.coerceAtMost(right.coerceAtMost(curCell))
            }
            arr = cur
        }
        var min = Int.MAX_VALUE
        for (i in 0 until l) {
            if (arr[i] < min) {
                min = arr[i]
            }
        }
        return min
    }
}

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