The given code calculates the sum of the elements on...

The given code calculates the sum of the elements on both the primary diagonal and the secondary diagonal of a square matrix (a 2D array). Here's a detailed explanation of what it does:

Detailed Breakdown:

1. Loop through each row of the matrix:

   for(int i=0; i<matrix.length; i++) { ... }
   

   Here, i represents the row and column indexes, since the matrix is square (meaning the number of rows equals the number of columns).

2. Add primary diagonal element:

   s = s + matrix[i][i];
   

   This line adds the element located on the primary diagonal to the sum s. The primary diagonal consists of elements where the row and column indices are the same, i.e., matrix[0][0], matrix[1][1], etc.

3. Add secondary diagonal element (if not overlapping):

   if(i != matrix.length - 1 - i) {
       s = s + matrix[i][matrix.length - i - 1];
   }
   

   This checks whether the current index i corresponds to the center of the matrix (applies when the primary and secondary diagonals intersect, which happens in matrices with odd dimensions).

   • If there's no overlap (i is not equal to matrix.length - 1 - i), add the element on the secondary diagonal located at [i][matrix.length - 1 - i].
   • The secondary diagonal consists of elements where the row index i and column index matrix.length - 1 - i add up to matrix.length - 1, such as matrix[0][n-1], matrix[1][n-2], etc.

4. Return the total sum:

   return s;
   

   After the loop finishes, s contains the sum of all elements on both diagonals, ensuring that overlapping elements (if any) are not added twice.

Example:

Suppose matrix is:

1  2  3
4  5  6
7  8  9

• Primary diagonal: 1, 5, 9
• Secondary diagonal: 3, 5, 7

The code calculates 1 + 5 + 9 + 3 + 7 = 25. The center element 5 (intersection of the two diagonals) is not added twice.

Key Assumptions:

• The matrix is a square matrix.
• s is initially defined and initialized outside the loop.