G* Get the pair of a sorted list of which the sum is given.

#include <iostream>

using namespace std;

int closestSmallerSearch(int[], int, int);

bool hasPair(int[], int, int[], int);

int main(void)

{
    int size = 0;

    cout << "How many elements? : ";
    cin >> size;

    int *arr = new int[size];
    int pairs[2] = { 0 };

    for (int i = 0; i < size; i++)
    {
        cout << "\nElement no:" << i + 1 << " = ";
        cin >> arr[i];
    }

    cout << "\n---------------------\n";

    cout << "\nGiven sum : ";
    int sum = 0; cin >> sum;

    if (hasPair(arr, size, pairs, sum))
    {
        cout << "\nFirst occurence of pair : (" << pairs[0] << ", " << pairs[1] << ")\n\n";
    }
    else
    {
        cout << "\nNo such pair is found.\n\n";
    }

    return 0;
}

int closestSmallerSearch(int list[], int size, int value)
{
    int low = 0, high = size - 1;
    int mid = 0;

    while (low <= high)
    {
        mid = low + ((high - low) / 2); // (low + high) / 2

        if (list[mid] == value)
        {
            return (mid - 1); // if matches then we need the index - 1 here
        }
        else if (list[mid] < value)
        {
            low = mid + 1;
        }
        else
        {
            high = mid - 1;
        }
    }

    if (low == high) // if not matches , we need the smaller nearest
    {
        if (list[low] < list[mid])
        {
            return low;
        }
        else if (list[low] > list[mid])
        {
            return (low - 1);
        }
    }
}

bool hasPair(int collection[], int size, int pairs[], int sum)

{
    bool pairFound = false;
    int begin = 0, end = closestSmallerSearch(collection, size, sum);
    if (end != -1)
    {
        while (begin < end) {
            int total = collection[begin] + collection[end];
            if (total == sum)
            {
                pairs[0] = collection[begin];
                pairs[1] = collection[end];
                pairFound = true;
                break;
            }
            else if (total < sum)
            {
                begin++;
            }
            else
            {
                end--;
            }
        }
    }
    else
    {
        cout << "\nGiven sum is too small." << end;
    }
    return pairFound;
}