Number Of Pairs With Given Sum

You have been given an integer array/list(arr) and a number 'Sum'. Find and return the total number of pairs in the array/list which when added, results equal to the 'Sum'.

Note:

Given array/list can contain duplicate elements.

(arr[i],arr[j]) and (arr[j],arr[i]) are considered same.

Input format :

The first line contains 2 space-separated integers N and Sum.

The next line contains N space-separated integers representing array elements.

Output format :

Print the total number of pairs present in the array/list.

Constraints :

1 <= N <= 10^5
-10^4 <= Sum <= 10^4
-10^4 <=  arr[ i ] <= 10^4

Time Limit: 1 sec

Sample Input 1:

9 12
1 3 6 2 5 4 3 2 4

Sample Output 1:

0

 Explanation For Sample Input 1:

Since there doesn't exist any pair with a sum equal to 12, so we print 0.

Sample Input 2:

6 10
2 8 10 5 -2 5

Sample Output 2:

2