diag-sum.js

// 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

// my solution
var diagonalSum = function(mat) {
    let sum = 0; 
    const n = mat.length;
    for (let i = 0; i < n; i++){
        sum+= mat[i][i]
    }

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

    if (n % 2 === 1){
        sum -= mat[Math.floor(n / 2)][Math.floor(n / 2)]
    }

    return sum
};