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

解題

func minFallingPathSum(matrix [][]int) int {
    if len(matrix) == 1 {
        return matrix[0][0]
    }

    for i := 1; i < len(matrix); i++ {
        for j := 0; j < len(matrix[0]); j++ {
            if j == 0 {
                matrix[i][j] += min(matrix[i - 1][j], matrix[i - 1][j + 1])
            } else if j == len(matrix[0]) - 1 {
                matrix[i][j] += min(matrix[i - 1][j], matrix[i - 1][j - 1])
            } else {
                matrix[i][j] += min(matrix[i - 1][j], min(matrix[i - 1][j + 1], matrix[i - 1][j - 1]))
            }
        }
    }

    min := matrix[len(matrix) - 1][0]
    for i := 0; i < len(matrix[0]); i++ {
        if matrix[len(matrix) - 1][i] < min {
            min = matrix[len(matrix) - 1][i]
        }
    }

    return min
}

func min(a, b int) int {
    if a < b { return a }
    return b
}