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Maximum Sum of an Hourglass

You are given an m x n integer matrix grid.

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.

Maximum Sum of an Hourglass diagram

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

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