2428. Maximum Sum of an Hourglass

Medium

You are given an m x n integer matrix grid.

We define an hourglass as a part of the matrix with the following form:

Return the maximum sum of the elements of an hourglass.

Note that an hourglass cannot be rotated and must be entirely contained within the matrix.

Example 1:

Input: grid = [[6,2,1,3],[4,2,1,5],[9,2,8,7],[4,1,2,9]]
Output:
 30
Explanation:
 The cells shown above represent the hourglass with the maximum sum: 6 + 2 + 1 + 2 + 9 + 2 + 8 = 30.

Example 2:

Input: grid = [[1,2,3],[4,5,6],[7,8,9]]
Output:
 35
Explanation:
 There is only one hourglass in the matrix, with the sum: 1 + 2 + 3 + 5 + 7 + 8 + 9 = 35.

Constraints:

• m == grid.length

• n == grid[i].length

• 3 <= m, n <= 150

• 0 <= grid[i][j] <= 10^6

解題

func maxSum(grid [][]int) int {
    max := 0
    for i := 1; i < len(grid) - 1; i++ {
        for j := 1; j < len(grid[0]) - 1; j++ {
            sum := grid[i][j] + grid[i - 1][j] + grid[i + 1][j] + grid[i - 1][j - 1] + grid[i - 1][j + 1] + grid[i + 1][j - 1] + grid[i + 1][j + 1]
            if sum > max {
                max = sum
            }
        }
    }

    return max
}