Why Practice Two Pointers?
The Two Pointers pattern is one of the highest-yield techniques in coding interviews. It allows you to transform nested-loop $O(n^2)$ solutions into efficient linear $O(n)$ ones.
Hand-Picked Problems
| Problem | Difficulty | Key Pattern |
|---|---|---|
| Two Sum II - Input Array Is Sorted | Easy | Opposite Direction |
| Valid Palindrome | Easy | Palindrome Check |
| Remove Duplicates from Sorted Array | Easy | Same-Direction (Write Pointer) |
| Squares of a Sorted Array | Easy | Squaring and Merging |
| Move Zeroes | Easy | Same-Direction |
| 3Sum | Medium | Sorting + Opposite Direction |
| Container With Most Water | Medium | Greedy Pointer Move |
| Sort Colors (Dutch National Flag) | Medium | Three Pointers |
| Subarray Product Less Than K | Medium | Sliding Window Hybrid |
| Trapping Rain Water | Hard | Extreme Boundaries |
Reflection Framework
For each problem you solve, write down:
- Pointer Initialization: Where did they start?
- Move Logic: Why did I move $L$ or $R$?
- Exit Condition: When did the loop stop?
- Complexity: Why is it $O(n)$?
Final Takeaway
Mastering these 10 problems will cover 90% of Two Pointer variations you'll see in FAANG interviews.