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Count pairs with given sum
Easy Accuracy: 41.59% Submissions: 100k+ Points: 2

Given an array of N integers, and an integer K, find the number of pairs of elements in the array whose sum is equal to K.

Example 1:

Input:
N = 4, K = 6
arr[] = {1, 5, 7, 1}
Output: 2
Explanation:
arr + arr = 1 + 5 = 6
and arr + arr = 5 + 1 = 6.


Example 2:

Input:
N = 4, K = 2
arr[] = {1, 1, 1, 1}
Output: 6
Explanation:
Each 1 will produce sum 2 with any 1.

You don't need to read input or print anything. Your task is to complete the function getPairsCount() which takes arr[], n and as input parameters and returns the number of pairs that have sum K.

Expected Time Complexity: O(N)
Expected Auxiliary Space: O(N)

Constraints:
1 <= N <= 105
1 <= K <= 108
1 <= Arr[i] <= 106

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