1572_MatrixDiagonalSum - a920604a/leetcode GitHub Wiki

class Solution {
public:
    int diagonalSum(vector<vector<int>>& mat) {
        int n = mat.size(), idx = 0, ret = 0;
        for(int i=0;i<n;++i){
            ret+=mat[i][idx];
            if(idx != n-1-idx) ret+=mat[i][n-1-idx];
            idx++;
        }
        return ret;
    }
};