Remove Duplicates from a Sorted Array — The Two-Pointer Technique

Sat, 09 Aug 2025 00:00:00 +0000

Removing duplicates from a sorted array is one of those problems that sounds trivial until you add the constraint: do it in-place, without allocating another array. That constraint is what makes it interesting and what makes the two-pointer pattern the right tool.

The problem: given a sorted integer array nums, remove duplicates in-place so each unique element appears exactly once. Return k — the count of unique elements. The values at nums[0] through nums[k-1] must be the unique elements in order; anything beyond index k-1 doesn’t matter.

Solving LeetCode's Valid Parentheses Problem with a Stack in Java

Wed, 06 Aug 2025 00:00:00 +0000

Some LeetCode problems feel like busy work. The Valid Parentheses problem is not one of them. It’s a clean, well-defined problem that teaches a genuinely useful pattern — the stack — and produces code that’s actually elegant when you get it right.

The problem: given a string containing only (, ), {, }, [, and ], determine if the input is valid. A string is valid if every opening bracket is closed by the correct bracket type, in the correct order.

Algorithms on

Remove Duplicates from a Sorted Array — The Two-Pointer Technique

Solving LeetCode's Valid Parentheses Problem with a Stack in Java