Topics / Two Pointers
↔️
Two Pointers
Two indices walking an array — the technique behind 3Sum, palindrome checks, and container problems.
Why learn Two Pointers?
-
Converts many O(n²) brute forces into O(n) one-pass solutions.
-
A single pattern that unlocks 30+ classic problems.
-
Appears constantly in mid-level interviews.
What you can build with Two Pointers
Sorted-array pair / triple problems Palindrome and substring checks In-place array modification (remove duplicates, move zeros)
Two Pointers tutorials
4 articlesHand-written tutorials, ordered as a recommended learning path.
- 01 Two Pointers A practical guide to the two pointers technique — opposite-end and same-direction patterns, when to use each, and six classic interview problems with worked solutions.
- 02 3Sum A careful walkthrough of LeetCode 15 3Sum using sort plus two pointers. We handle duplicate triplets cleanly and avoid the classic off-by-one traps.
- 03 Container Water Solve LeetCode 11 Container With Most Water with the two-pointer technique. We prove correctness and contrast it with the quadratic brute force.
- 04 Trapping Rain Water Solve LeetCode 42 Trapping Rain Water in linear time and constant space using the two-pointer technique. Brute force, optimal walkthrough, and interview talk track.