LeetCode Swift Solutions ​

This section explains common LeetCode problems using Swift. The goal is not only to show a final answer, but to make the reasoning clear enough that you can rebuild the solution during an interview.

Every problem page is written around the same structure: what the problem is asking, the core idea, step-by-step reasoning, Swift implementation notes, complexity, and edge cases to remember. That makes the pages useful for both quick review and slower study.

How To Use These Solutions ​

1. Read the problem summary and identify the pattern: hash map, two pointers, sorting, set lookup, or bucket counting.
2. Try to explain the approach before looking at the code.
3. Walk through at least one sample input by hand.
4. Study the Swift-specific details, especially dictionary updates, array mutation, and character handling.
5. Re-implement the solution without copying it.

Problem Index ​

• • 1. Two Sum

• • 125. Valid Palindrome

• • 128. Longest Consecutive Sequence

• • 15. 3Sum

• • 167. Two Sum II - Input Array Is Sorted

• • 217. Contains Duplicate

• • 242. Valid Anagram

• • 283. Move Zeroes

• • 344. Reverse String

• • 347. Top K Frequent Elements

Core Patterns Covered ​

• Hash map lookup for complements and frequency counts
• Two-pointer scans on sorted arrays and character arrays
• In-place array mutation
• Set-based sequence detection
• Sorting with duplicate skipping
• Bucket-based frequency selection

For language foundations, review Swift collection types, Swift strings and characters, and Swift control flow.

Last updated: June 27, 2026