Count Pairs with Given Sum

Given an integer array/list arr and an integer 'Sum', determine the total number of unique pairs in the array whose elements sum 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 elements of the array.

Output:

Output a single integer, representing the total number of pairs whose sum is equal to 'Sum'.

Example:

Input: 5 7 1 2 3 4 3 Output: 2

Constraints:

1 ≤ N ≤ 10⁵

-10⁴ ≤ Sum ≤ 10⁴

-10⁴ ≤ arr[i] ≤ 10⁴

Time Limit: 1 sec

Note:

Array may contain duplicate elements. The pairs (arr[i], arr[j]) and (arr[j], arr[i]) are considered the same.

Question

Count Pairs with Given Sum

Given an integer array/list arr and an integer 'Sum', determine the total number of unique pairs in the array whose elements sum 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 elements of the array.

Output:

Output a single integer, representing the total number of pairs whose sum is equal to 'Sum'.

Example:

Input:
5 7
1 2 3 4 3
Output:
2

Constraints:

1 ≤ N ≤ 10⁵
-10⁴ ≤ Sum ≤ 10⁴
-10⁴ ≤ arr[i] ≤ 10⁴
Time Limit: 1 sec

Note:

Array may contain duplicate elements.
The pairs (arr[i], arr[j]) and (arr[j], arr[i]) are considered the same.

Accepted Answer

Count the total number of unique pairs in an array whose elements sum up to a given value.

Use a hashmap to store the frequency of each element in the array.
Iterate through the array and for each element, check if (Sum - current element) exists in the hashmap.
Increment the count of pairs if the complement exists in the hashmap.
Divide the count by 2 to avoid counting duplicates like (arr[i], arr[j]) and (arr[j], arr[i]) separately.