hourglass.java

/*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] <= 106*/ 


public int maxSum(int[][] grid) {
       int ans = 0;
       for(int i = 0; i < grid.length - 2; i ++) {
           for(int j = 0; j < grid[0].length - 2; j ++) {
               int sum = grid[i][j] + grid[i][j + 1] + grid[i][j + 2] + grid[i + 1][j + 1] + grid[i + 2][j] + grid[i + 2][j + 1] + grid[i + 2][j + 2];
                ans = Math.max(ans, sum);
           } 
       }
       return ans; 
    }