HackMD
HashMap Study Guide
Basic HashMap Operations
Fundamental problems that introduce the concept and basic usage of hash maps.
- 🟩 1. Two Sum [Solution]
- 🟩 217. Contains Duplicate [Solution]
- 🟩 219. Contains Duplicate II [Solution]
- 🟨 274. H-Index [Solution]
- 🟩 1460. Make Two Arrays Equal by Reversing Subarrays [Solution]
- 🟩 2053. Kth Distinct String in an Array [Solution]
String Manipulation with HashMap
Problems involving the use of hash maps for efficient string processing.
- 🟨 49. Group Anagrams [Solution]
- 🟩 242. Valid Anagram [Solution]
- 🟩 383. Ransom Note [Solution]
- 🟩 409. Longest Palindrome [Solution]
Pattern Matching
Problems that involve identifying patterns or relationships between elements using hash maps.
Sequence and Array Problems
Complex problems involving sequences or arrays that can be efficiently solved using hash maps.
- 🟥 41. First Missing Positive [Solution]
- 🟨 128. Longest Consecutive Sequence [Solution]
- 🟨 525. Contiguous Array [Solution]
Geometric Problems
Problems involving geometric concepts that can be solved efficiently using hash maps.
Frequency Counting
Problems that involve counting the frequency of elements, often solved efficiently with hash maps.
Cycle Detection
Problems involving detecting cycles in sequences or graphs using hash maps.
Ordered Map Applications
Problems that benefit from using ordered maps (like TreeMap in Java or SortedDict in Python).
Problem Difficulty Legend
- 🟩 Easy
- 🟨 Medium
- 🟧 Medium-Hard
- 🟥 Hard
- ⬛ Very Hard
