Diagonal elementlar yig'indisi

N × N o'lchamli kvadrat matrix matritsasi berilgan. Bosh diagonaldagi (matrix[i][i]) elementlar yig'indisini toping.

func diagonalSum(N int, matrix [][]int) int {
    // ...
}

Misollar

Input: N=3, matrix=[[1,2,3],[4,5,6],[7,8,9]]
Output: 15

Input: N=4, matrix=[[1,0,0,0],[0,2,0,0],[0,0,3,0],[0,0,0,4]]
Output: 10

Input: N=2, matrix=[[5,10],[15,20]]
Output: 25

Maslahatlar

1. Bosh diagonaldagi elementlarda qator va ustun indekslari teng.
2. Bitta sikl yetadi: sum += matrix[i][i].