two_pointer_technique.cpp

// C++ Program Illustrating Naive Approach to
// Find if There is a Pair in A[0..N-1] with Given Sum
// Using Two-pointers Technique
 
// Importing required libraries
#include <bits/stdc++.h>
 
using namespace std;
 
// Two pointer technique based solution to find
// if there is a pair in A[0..N-1] with a given sum.
int isPairSum(int A[], int N, int X)
{
    // represents first pointer
    int i = 0;
 
    // represents second pointer
    int j = N - 1;
 
    while (i < j) {
 
        // If we find a pair
        if (A[i] + A[j] == X)
            return 1;
 
        // If sum of elements at current
        // pointers is less, we move towards
        // higher values by doing i++
        else if (A[i] + A[j] < X)
            i++;
 
        // If sum of elements at current
        // pointers is more, we move towards
        // lower values by doing j--
        else
            j--;
    }
    return 0;
}
 
// Driver code
int main()
{
    // array declaration
    int arr[] = { 2, 3, 5, 8, 9, 10, 11 };
     
    // value to search
    int val = 17;
     
    // size of the array
    int arrSize = *(&arr + 1) - arr;
     
      // array should be sorted before using two-pointer technique
      sort(arr, arr+7);
   
    // Function call
    if((bool)isPairSum(arr, arrSize, val)==1)
    {
        cout<<"Valid Pair present";
    }
    else
    {
        cout<<"No Valid Pair found";
    }
 
    return 0;
}