Matrix_Diagonal_Sum.java

// Given a square matrix mat, return the sum of the matrix diagonals.

// Only include the sum of all the elements on the primary diagonal and all the elements on the secondary diagonal that are not part of the primary diagonal.

// Example 1:


// Input: mat = [[1,2,3],
//               [4,5,6],
//               [7,8,9]]
// Output: 25
// Explanation: Diagonals sum: 1 + 5 + 9 + 3 + 7 = 25
// Notice that element mat[1][1] = 5 is counted only once.
// Example 2:

// Input: mat = [[1,1,1,1],
//               [1,1,1,1],
//               [1,1,1,1],
//               [1,1,1,1]]
// Output: 8
// Example 3:

// Input: mat = [[5]]
// Output: 5

class Solution {
    public int diagonalSum(int[][] mat) {
        int n = mat.length;
        int sum = 0;

        for(int i=0;i<n;i++){
            sum += mat[i][i];
            sum += mat[i][n-i-1];

        }
        if(n%2 == 1){
            sum -= mat[n/2][n/2];
        }
        return sum;
    }
}