8

Number Of Pairs With Given Sum

Difficulty: MEDIUM
Contributed By
Anish De |Level 1
Avg. time to solve
39 min
Success Rate
60%

Problem Statement

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
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