Question

Find pair in array whose sum is equal to given number

Answer 1

Given an array A[] and a number x, check for pair in A[] with sum as x

Write a program that, given an array A[] of n numbers and another number x, determines whether or not there exist two elements in S whose sum is exactly x.

Recommended: Please solve it on “PRACTICE ” first, before moving on to the solution.

METHOD 1 (Use Sorting)

Algorithm :

hasArrayTwoCandidates (A[], ar_size, sum)

1) Sort the array in non-decreasing order.

2) Initialize two index variables to find the candidate

elements in the sorted array.

(a) Initialize first to the leftmost index: l = 0

(b) Initialize second the rightmost index: r = ar_size-1

3) Loop while l < r.

(a) If (A[l] + A[r] == sum) then return 1

(b) Else if( A[l] + A[r] < sum ) then l++

(c) Else r--

4) No candidates in whole array - return 0

Time Complexity: Depends on what sorting algorithm we use. If we use Merge Sort or Heap Sort then (-)(nlogn) in worst case. If we use Quick Sort then O(n^2) in worst case.

Auxiliary Space : Again, depends on sorting algorithm. For example auxiliary space is O(n) for merge sort and O(1) for Heap Sort.

PLEASE MAKE ME AS A BRAINLIST ANSWER