Matrix Diagonal Sum

export function diagonalSum(mat: number[][]): number {
  const n = mat.length;
 
  let result = 0;
  for (let i = 0; i < n; i++) {
    if (i === n - i - 1) {
      result += mat[i][i];
    } else {
      result += mat[i][i] + mat[i][n - i - 1];
    }
  }
 
  return result;
}