Let X = {x1, x2, ..., xn} be an array of n positive integers and a is an integer. Propose an efficient algorithm to determine whether there are two elements in X whose sum is exactly a. Derive the time-complexity of the proposed algorithm. code example

Example: find pair in unsorted array which gives sum x

// C++ program to check if given array 
// has 2 elements whose sum is equal 
// to the given value 
  
#include <bits/stdc++.h> 
using namespace std; 
  
// Function to check if array has 2 elements 
// whose sum is equal to the given value 
bool hasArrayTwoCandidates(int A[], int arr_size, 
                           int sum) 
{ 
    int l, r; 
  
    /* Sort the elements */
    sort(A, A + arr_size); 
  
    /* Now look for the two candidates in  
       the sorted array*/
    l = 0; 
    r = arr_size - 1; 
    while (l < r) { 
        if (A[l] + A[r] == sum) 
            return 1; 
        else if (A[l] + A[r] < sum) 
            l++; 
        else // A[i] + A[j] > sum 
            r--; 
    } 
    return 0; 
} 
  
/* Driver program to test above function */
int main() 
{ 
    int A[] = { 1, 4, 45, 6, 10, -8 }; 
    int n = 16; 
    int arr_size = sizeof(A) / sizeof(A[0]); 
  
    // Function calling 
    if (hasArrayTwoCandidates(A, arr_size, n)) 
        cout << "Array has two elements with given sum"; 
    else
        cout << "Array doesn't have two elements with given sum"; 
  
    return 0; 
}