Leetcode Brush Questions--Sum of Diagonal Elements of Matrix

answer:

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 != 0){
            sum -= mat[n/2][n/2];
        }
        return sum;
    }
}