Row-wise common elements in two diagonals of a square matrix

Given a square matrix, find out count of numbers that are same in same row and same in both primary and secondary diagonals.

Examples : 

Input : 1 2 1
 4 5 2
 0 5 1
Output : 2
Primary diagonal is 1 5 1
Secondary diagonal is 1 5 0
Two elements (1 and 5) match 
in two diagonals and same.

Input : 1 0 0
 0 1 0
 0 0 1
Output : 1
Primary diagonal is 1 1 1
Secondary diagonal is 0 1 0
Only one element is same.

We can achieve this in O(n) time, O(1) space and only one traversal. We can find current element in i-th row of primary diagonal as mat[i][i] and i-th element of secondary diagonal as mat[i][n-i-1]. 

Implementation:

1

Time Complexity: O(n). 
Auxiliary Space: O(1).