Today I have done leetcode's May LeetCoding Challenge with cpp.

May LeetCoding Challenge 8

Description

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

Solution

auto speedup = [](){
  cin.tie(nullptr);
  cout.tie(nullptr);
  ios::sync_with_stdio(false);
  return 0;
}();
class Solution {
public:
  int diagonalSum(vector<vector<int>>& mat) {
    int len = mat.size();
    int sum = 0;
    for(int i = 0; i < len; ++i) {
      sum += mat[i][i] + mat[i][len - 1 - i];
    }
    if(len & 1) sum -= mat[len/2][len/2];
    return sum;
  }
};

// Accepted
// 113/113 cases passed (16 ms)
// Your runtime beats 52.8 % of cpp submissions
// Your memory usage beats 17.56 % of cpp submissions (11.4 MB)