LeetCode-in-Java

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

public class Solution {
    public int minFallingPathSum(int[][] matrix) {
        int l = matrix[0].length;
        int[] arr = matrix[0];
        for (int i = 1; i < matrix.length; i++) {
            int[] cur = new int[l];
            for (int j = 0; j < l; j++) {
                int left = Integer.MAX_VALUE;
                int right = Integer.MAX_VALUE;
                int curCell = arr[j];
                if (j > 0) {
                    left = arr[j - 1];
                }
                if (j < l - 1) {
                    right = arr[j + 1];
                }
                cur[j] = matrix[i][j] + Math.min(left, Math.min(right, curCell));
            }
            arr = cur;
        }
        int min = Integer.MAX_VALUE;
        for (int i = 0; i < l; i++) {
            if (arr[i] < min) {
                min = arr[i];
            }
        }
        return min;
    }
}

This site is open source. Improve this page.