2428. Maximum Sum of an Hourglass

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 hou