Find four elements a, b, c and d in an array such that a+b = c+d - GeeksforGeeks



Find four elements a, b, c and d in an array such that a+b = c+d - GeeksforGeeks

Find four elements a, b, c and d in an array such that a+b = c+d

Given an array of distinct integers, find if there are two pairs (a, b) and (c, d) such that a+b = c+d, and a, b, c and d are distinct elements. If there are multiple answers, then print any of them.

Example:

Input:   {3, 4, 7, 1, 2, 9, 8}  Output:  (3, 8) and (4, 7)  Explanation: 3+8 = 4+7    Input:   {3, 4, 7, 1, 12, 9};  Output:  (4, 12) and (7, 9)  Explanation: 4+12 = 7+9    Input:  {65, 30, 7, 90, 1, 9, 8};  Output:  No pairs found  

Expected Time Complexity: O(n2)

We strongly recommend you to minimize your browser and try this yourself first.

A Simple Solution is to run four loops to generate all possible quadruples of array element. For every quadruple (a, b, c, d), check if (a+b) = (c+d). Time complexity of this solution is O(n4).

An Efficient Solution can solve this problem in O(n2) time. The idea is to use hashing. We use sum as key and pair as value in hash table.


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