Find Pairs in Array with Given Sum in C++
Pairs in Array with given Sum
On this page, we will look into a coding question where we will learn how to Find Pairs in Array with given sum in C++ Programing Language. There might be different approaches to solve this question, one you will find here. If your approach is a bit different post it in the comment section.
Find Pairs in Array with given Sum in C++
To find pairs in an array with a given sum in C, we can use two methods
- Brute Force (Time complexity: O(n^2) )
- Using Sorting (Time complexity: O(n log n) )
Both methods have their own pros and cons. The brute force method can be slow for large arrays but it is very simple and easy to implement . The sorting method is faster for large arrays, but requires extra space for sorting and modifying the original array.
Method 1 : Brute Force Method
- In this approach, we check every pair of elements in the array to see if their sum is equal to the given target sum.
- This method has a time complexity of O(n^2) as we have to compare each element with every other element
C++ code for brute force
Run
#include <iostream>
using namespace std;
void findPairs (int arr[], int n, int targetSum)
{
for (int i = 0; i < n - 1; i++)
{
for (int j = i + 1; j < n; j++)
{
if (arr[i] + arr[j] == targetSum)
{
cout << "Pair found at index " << i << " and " << j << endl;
}
}
}
}
int main ()
{
int arr[] = { 5, 8, 1, 4, 6, 3, 2, 7 };
int n = sizeof (arr) / sizeof (arr[0]);
int targetSum = 10;
findPairs (arr, n, targetSum);
return 0;
}
Output
Pair found at index 1 and 6 Pair found at index 3 and 4 Pair found at index 5 and 7
Method 2 : Sorting Method
- The array is first sorted in ascending order in the sorting technique.
- Then, we employ two pointers, one of which points to the first element and the other to the last element.
- These two pointers values are added, and we then check to see if the result equals the specified sum.
The left pointer is increased if the value is less than the total, and the right pointer is decreased if the value is higher. - This method has a time complexity of O(n log n) due to the sorting algorithm used.
C++ code for sorting method
Run
#include <iostream>
#include <algorithm>
using namespace std;
void findPairs (int arr[], int n, int targetSum)
{
sort (arr, arr + n);
int left = 0;
int right = n - 1;
while (left < right)
{
int currSum = arr[left] + arr[right];
if (currSum == targetSum)
{
cout << "Pair found: " << arr[left] << " and " << arr[right] <<
endl;
left++;
right--;
}
else if (currSum < targetSum)
{
left++;
}
else
{
right--;
}
}
}
int main ()
{
int arr[] = { 5, 8, 1, 4, 6, 3, 2, 7 };
int n = sizeof (arr) / sizeof (arr[0]);
int targetSum = 10;
findPairs (arr, n, targetSum);
return 0;
}
Output
Pair found: 2 and 8 Pair found: 3 and 7 Pair found: 4 and 6
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