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.lengthn == grid[i].length3 <= m, n <= 1500 <= grid[i][j] <= 10^6
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
}