✅ Find Pairs in Sorted Array with Given Sum in C++

Finding pairs in a sorted array that sum up to a specific target is a common problem in computer science. This tutorial demonstrates how to efficiently solve this using the two-pointer technique in C++.

📘 What You'll Learn

• Understanding the two-pointer technique
• Implementing an efficient solution in C++
• Optimizing time complexity to O(n)

📄 C++ Program: Find Pairs with Given Sum

#include <iostream>
#include <vector>
using namespace std;

void findPairsWithSum(const vector<int>& arr, int target) {
    int left = 0;
    int right = arr.size() - 1;
    bool found = false;

    while (left < right) {
        int sum = arr[left] + arr[right];
        if (sum == target) {
            cout << "Pair found: " << arr[left] << " + " << arr[right] << " = " << target << endl;
            found = true;
            left++;
            right--;
        } else if (sum < target) {
            left++;
        } else {
            right--;
        }
    }

    if (!found) {
        cout << "No pairs found with sum " << target << endl;
    }
}

int main() {
    vector<int> sortedArray = {1, 2, 3, 4, 5, 6, 7, 8, 9};
    int targetSum = 10;
    findPairsWithSum(sortedArray, targetSum);
    return 0;
}
      

✅ Sample Output

Pair found: 1 + 9 = 10
Pair found: 2 + 8 = 10
Pair found: 3 + 7 = 10
Pair found: 4 + 6 = 10
    

📘 Explanation

• Initialize two pointers: one at the start (left) and one at the end (right) of the array.
• Calculate the sum of the elements at these pointers.
• If the sum equals the target, print the pair and move both pointers inward.
• If the sum is less than the target, move theleftpointer to the right to increase the sum.
• If the sum is greater than the target, move therightpointer to the left to decrease the sum.
• Continue this process until theleftpointer is no longer less than therightpointer.