An hourglass in a grid is a group of seven cells shaped like this, anchored at some top-left cell:
a b c
d
e f g
Given a grid of integers grid with at least 3 rows and 3 columns, return the largest sum of any
hourglass that fits entirely inside the grid.
Examples
Input: grid = [[1, 1, 1, 0],
[0, 1, 0, 0],
[1, 1, 1, 0],
[0, 0, 0, 0]]
Output: 7
Explanation: the hourglass in the top-left corner sums 1+1+1 + 1 + 1+1+1.
Input: grid = [[-1, -1, -1],
[-1, -9, -1],
[-1, -1, -1]]
Output: -15
Constraints
3 <= rows, cols <= 100,-100 <= grid[r][c] <= 100
Goals
- Sum a fixed non-rectangular shape at every valid position
- Track a maximum that may be negative