Two pointer is really an easy and effective technique which is typically used for searching pairs in a sorted arrays.
Given a sorted array A (sorted in ascending order), having N integers, find if there exists any pair of elements (A[i], A[j]) such that their sum is equal to X.
Let’s see the naive solution.
The time complexity of this solution is O(n2).
Now let’s see how the two pointer technique works. We take two pointers, one representing the first element and other representing the last element of the array, and then we add the values kept at both the pointers. If their sum is smaller than X then we shift the left pointer to right or if their sum is greater than X then we shift the right pointer to left, in order to get closer to the sum. We keep moving the pointers until we get the sum as X.
The above solution works in O(n)
How does this work?
The algorithm basically uses the fact that input array is sorted. We start sum of extreme values (smallest and largest) and conditionally move both pointers. We move left pointer i when sum of A[i] and A[j[ is less than X. We do not miss any pair because sum is already smaller than X. Same logic applies for right pointer j.
More problems based on two pointer technique.
- Find the closest pair from two sorted arrays
- Find the pair in array whose sum is closest to x
- Find all triplets with zero sum
- Find a triplet that sum to a given value
- Find a triplet such that sum of two equals to third element
- Find four elements that sum to a given value
- Window Sliding Technique
- C++ Program to compare two string using pointers
- Program to reverse an array using pointers
- Pair with largest sum which is less than K in the array
- Find prime numbers in the first half and second half of an array
- Find the difference of count of equal elements on the right and the left for each element
- Minimum number of times A has to be repeated such that B is a substring of it
- Smallest element greater than X not present in the array
- Count of elements that can be deleted without disturbing the mean of the initial array
- Maximum sum combination from two arrays
- Find maximum xor of k elements in an array
- All unique combinations whose sum equals to K
- Find the sum of the first half and second half elements of an array
- Introduction to Data Structures | 10 most commonly used Data Structures
This article is contributed by Rohan Das. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to firstname.lastname@example.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.