Find four elements that sum to a given value | Set 3 (Hashmap)

Given an array of integers, Check if there exist four elements at different indexes in the array whose sum is equal to a given value k.
For example, if the given array is {1 5 1 0 6 0} and k = 7, then your function should print “YES” as (1+5+1+0=7).

Examples:

Input  : arr[] = {1 5 1 0 6 0} 
             k = 7
Output : YES

Input :  arr[] = {38 7 44 42 28 16 10 37 
                  33 2 38 29 26 8 25} 
            k = 22
Output : NO

We have discussed different solutions in below two sets.
Find four elements that sum to a given value | Set 1 (n^3 solution)
Find four elements that sum to a given value | Set 2 ( O(n^2Logn) Solution)

In this post, an optimized solution is discussed that works in O(n²) on average.

The idea is to create a hashmap to store pair sums.

Loop i = 0 to n-1 :
 Loop j = i + 1 to n-1  
   calculate sum = arr[i] + arr[j]
     If (k-sum) exist in hash 
      a) Check in hash table for all
         pairs of indexes which form
         (k-sum).
      b) If there is any pair with no 
         no common indexes.
           return true 
    Else  update hash table
    EndLoop;
EndLoop;

Output:

YES

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