intro practice · coding problem
Valid Palindrome
LeetCode #125 — Valid Palindrome. Solve on LeetCode, then implement here if you want it in your drill queue. https://leetcode.com/problems/valid-palindrome/
The mechanism
Two pointers replace a nested loop with a single pass by exploiting structure — usually a sorted array or a sequence with a monotonic property. The pointers move toward or away from each other based on a comparison, so each element is visited once.
Expected evidence
Pass all LeetCode test cases for this problem.
Try this drill in the practice workspace →
Hints when you need them
- Pattern hint: two pointers.
- Start with brute force, then optimize time/space.
- Write down invariants before coding.
Watch for these mistakes
- Using two pointers on unsorted data when the technique needs order
- Off-by-one errors at the start/end conditions
- Moving the wrong pointer and skipping valid pairs