1572. Matrix Diagonal Sum

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
 

Constraints:

n == mat.length == mat[i].length
1 <= n <= 100
1 <= mat[i][j] <= 100

根据对角线算出坐标，然后在奇数的场景下只加一次即可。

class MatrixDiagonalSum : public Solution {
public:
    void Exec() {
    }
    int diagonalSum(vector<vector<int>>& mat) {
        int sum = 0;
        int r1 = 0, c1 = 0, r2 = 0, c2 = mat.size() - 1;
        for (int i = 0; i < mat.size(); i++) {
            sum += mat[r1][c1];
            if (!(mat.size() % 2 != 0 && r2 == r1 && c2 == c1)) {
                sum += mat[r2][c2];
            }
            r1++; c1++;
            r2++; c2--;
        }
        return sum;
    }
};