ForgeAlgo - Two Pointers
Estimated Time: 5 min
Tech Stack: Java
Keywords: Data Structure - Algorithms
Experience Level: Beginner - Advanced
š¹ Step 1: Understanding the Two-Pointer Technique
Two pointers refer to using two indices to traverse a data structure efficiently. There are different variations of
this approach. The most common are:
Opposite Ends(Left-Right Pointers) ā Used for problems like palindrome check, sorting, and pair sum.Same Direction(Fast-Slow Pointers) ā Used for linked lists (detecting cycles), sliding window, and merging sorted arrays.
šÆ Summary of Two-Pointer Variations
| Variation | Use Case Example |
|---|---|
| Opposite Ends | Two Sum, Palindrome Check |
| Fast-Slow Pointers | Cycle Detection, Middle of List |
| Merging Two Pointers | Merge Sort, Merge Arrays |
| Sliding Window | Longest Substring, Sub arrays |
| Removing Elements | Remove Duplicates, Filtering |
| Reverse Two-Pointer | Reverse String, Reverse List |
š¹ Step 2: Identifying When to Use It
You can use Two-Pointer when:
- ā The problem involves sorted arrays or linked lists.
- ā You need to compare elements at different positions.
- ā A nested loop (O(nĀ²)) solution exists, and you want to optimize it.
- ā It involves pairing elements, finding a sub-array, or checking conditions between two elements.
šÆ Final Thoughts
The Two-Pointer technique is highly adaptable and can be combined with other techniques to optimize solutions across
arrays, graphs, bit manipulation, and dynamic programming.