Blind 75 Two Pointer Questions
3 problems · Free practice
Two pointers reduce the search space by moving through a sequence in a deliberate order. The difficult part is explaining why a discarded position cannot improve the answer. Compare character pairs in a palindrome, use sorted order to find a target sum, and reason about which boundary limits a container.
Practice two pointers
Valid Palindrome
EasyCheck whether a string reads the same in both directions after ignoring non-alphanumeric characters and letter case. An empty cleaned string counts as a palindrome.
3Sum
MediumReturn every distinct triplet of values in an integer array that sums to zero. A triplet uses three different indices; duplicate value-triplets should appear once.
Container With Most Water
MediumVertical lines stand at consecutive integer x-coordinates with nonnegative heights. Choose two lines that hold the greatest area of water with the x-axis; the water height is the shorter line.
What to focus on
- Write the condition that makes each pointer move safe.
- For 3Sum, separate duplicate handling from the sum comparison.
- Check whether sorting changes the required output or mutates the input.