Remove Duplicates from Sorted Array in Java
This is the array version of sorted duplicate compaction. Because the input is sorted, duplicates appear in blocks, which makes one-pass in-place deduplicati...
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Remove All Adjacent Duplicates in String (Java)
This problem looks like repeated string cleanup, but the real pattern is stack simulation. Whenever a new character cancels the previous one, we want to “und...
Palindrome Number in Java (Without String Conversion)
This problem looks like a string problem at first, but there is a neat numeric solution. The clean trick is to reverse only half of the digits instead of rev...
Middle of the Linked List in Java
This is one of the best introductory fast-and-slow pointer problems. It looks simple, but it teaches a pattern that later shows up in cycle detection, palind...
Longest Substring Without Repeating Characters in Java
This is one of the most important sliding-window problems. The goal is not to generate every substring, but to maintain one valid window whose characters are...