- no duplicated in hashset
If you’re preparing for coding interviews, HashMap-based problems are frequently asked in top companies like Google, Amazon, Microsoft, Facebook, and Apple. Here are some of the most popular LeetCode HashMap questions categorized by difficulty level:
🔥 Easy HashMap Questions
- Two Sum (LC #1)
- Concepts: HashMap, Complementary Search
- Asked in: Amazon, Microsoft, Google
- Contains Duplicate (LC #217)
- Concepts: HashMap, HashSet
- Asked in: Google, Facebook, Apple
- Valid Anagram (LC #242)
- Concepts: HashMap, Frequency Count
- Asked in: Google, Amazon
- Intersection of Two Arrays (LC #349)
- Concepts: HashSet, HashMap
- Asked in: Apple, Uber, Google
- Majority Element (LC #169)
- Concepts: HashMap, Boyer-Moore Voting
- Asked in: Facebook, Amazon
⚡ Medium HashMap Questions
-
Group Anagrams (LC #49)
- Concepts: HashMap, Sorting as Key
- Asked in: Google, Microsoft, Facebook
-
Longest Substring Without Repeating Characters (LC #3)
- Concepts: HashMap, Sliding Window
- Asked in: Amazon, Facebook, Netflix
-
Subarray Sum Equals K (LC #560)
- Concepts: HashMap, Prefix Sum
- Asked in: Google, Microsoft, Uber
-
4Sum II (LC #454)
- Concepts: HashMap, Two-Pass Calculation
- Asked in: Google, Bloomberg
-
Word Pattern (LC #290)
- Concepts: HashMap, Bijective Mapping
- Asked in: Google, Uber
-
Isomorphic Strings (LC #205)
- Concepts: HashMap, Character Mapping
- Asked in: Facebook, Amazon
🚀 Hard HashMap Questions
-
Minimum Window Substring (LC #76)
- Concepts: HashMap, Sliding Window
- Asked in: Google, Microsoft, Facebook
-
Longest Consecutive Sequence (LC #128)
- Concepts: HashMap, Union-Find
- Asked in: Google, Amazon, Facebook
-
Substring with Concatenation of All Words (LC #30)
- Concepts: HashMap, Sliding Window
- Asked in: Google, Microsoft
-
Palindrome Pairs (LC #336)
- Concepts: HashMap, Trie
- Asked in: Google, Bloomberg
-
Alien Dictionary (Topological Sorting) (LC #269 - Premium)
- Concepts: HashMap, Graph, BFS/DFS
- Asked in: Facebook, Google
📌 Recommended Strategy to Solve These
-
Master HashMap Basics
- Key-value storage
- Hash collisions
- O(1) lookup and insertion
-
Understand Common HashMap Techniques
- Frequency Counting (e.g., Anagrams, Duplicates)
- Prefix Sum (e.g., Subarray Sum Equals K)
- Sliding Window (e.g., Longest Substring, Minimum Window Substring)
- Two-Pass HashMap (e.g., 4Sum II)
- Character Mapping (e.g., Isomorphic Strings, Word Pattern)
-
Practice Real-World Interview Problems
- Start with Easy problems to build intuition.
- Move to Medium problems focusing on sliding window and prefix sums.
- Finally, tackle Hard problems that involve Trie, Topological Sorting, and Advanced Graph Concepts.
Would you like detailed explanations or step-by-step solutions for any of these? 🚀