Find All Pairs with Given Sum

Given an integer array arr and an integer Sum, count and return the total number of pairs in the array whose elements add up to the given Sum.

Input:

The first line contains two space-separated integers N and Sum. The second line contains N space-separated integers representing the array elements.

Output:

Print the total number of pairs present in the array that add up to the given Sum.

Example:

Input:

N = 5, Sum = 7
arr = [1, 5, 3, 4, 2]

Output:

2

Explanation:

There are two pairs that add up to 7: (3, 4) and (5, 2).

Constraints:

• 1 <= N <= 10^5
• -10^4 <= Sum <= 10^4
• -10^4 <= arr[i] <= 10^4
• Time Limit: 1 sec

Note:

Arrays can contain duplicate elements. Pairs (arr[i],arr[j]) and (arr[j],arr[i]) are considered the same.