find a pair of elements from an array whose sum equals a given number code example

Example 1: Function to find a pair in an array with a given sum using hashing

def findPair(A, sum):
 
    # create an empty dictionary
    dict = {}
 
    # do for each element
    for i, e in enumerate(A):
 
        # check if pair `(e, sum-e)` exists
 
        # if the difference is seen before, print the pair
        if sum - e in dict:
            print("Pair found at index", dict.get(sum - e), "and", i)
            return
 
        # store index of the current element in the dictionary
        dict[e] = i
 
    # No pair with the given sum exists in the list
    print("Pair not found")

Example 2: 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  
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; 
}