[Solved] Any one explain how this works? [closed]

Question

The code calculates a number of even numbers (evenCount) and odd numbers (oddCount) in the array.

Every two even numbers make a pair that gives an even number in sum. The number of such pairs is evenCount * (evenCount - 1) /2. There is evenCount ways to select the first even number, evenCount - 1 to select the second and apparently (a, b) is the same pair as (b, a), so the division by two.

The same is with odd numbers. Every two odd numbers make a pair that gives an even number in sum.

This is how your get temp = (evenCount * (evenCount - 1) / 2) + (oddCount * (oddCount - 1) / 2).

Accepted Answer

The code calculates a number of even numbers (evenCount) and odd numbers (oddCount) in the array.

Every two even numbers make a pair that gives an even number in sum. The number of such pairs is evenCount * (evenCount - 1) /2. There is evenCount ways to select the first even number, evenCount - 1 to select the second and apparently (a, b) is the same pair as (b, a), so the division by two.

The same is with odd numbers. Every two odd numbers make a pair that gives an even number in sum.

This is how your get temp = (evenCount * (evenCount - 1) / 2) + (oddCount * (oddCount - 1) / 2).