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

Question

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.

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

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

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

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

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

Accepted Answer

Count and return the total number of pairs in the array whose elements add up to a given sum.

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.

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