top 10 map problems for FAANG Interview

Map (or HashMap / Dictionary) problems are core FAANG favorites because they test your understanding of hashing, frequency counting, lookup efficiency, and pattern recognition.

Here’s the Top 10 HashMap-based problems you should absolutely master before a FAANG interview 👇

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🧩 Top 10 Map (HashMap / Dictionary) Problems for FAANG Interviews

#	Problem	Pattern / Concept	Key Skills Tested	Difficulty
1️⃣	Two Sum	Value → Index mapping	Complement lookup	Easy
2️⃣	Group Anagrams	Map (sorted string → list of words)	Hashing complex keys	Medium
3️⃣	Top K Frequent Elements	Map + Min-Heap	Frequency counting	Medium
4️⃣	Subarray Sum Equals K	Prefix Sum + HashMap	Cumulative sum tracking	Medium–Hard
5️⃣	Longest Substring Without Repeating Characters	Sliding Window + Map	Index tracking, dynamic window	Medium
6️⃣	Word Pattern / Isomorphic Strings	Bidirectional Map	Character mapping consistency	Medium
7️⃣	Find Duplicate Subtrees / Logs / Files	Map (serialized structure → count)	Hashing non-trivial data	Hard
8️⃣	Valid Anagram	Frequency counting	Comparing maps	Easy
9️⃣	Longest Consecutive Sequence	HashSet / HashMap	O(n) sequence building	Medium
🔟	LRU Cache Implementation	Ordered Map + LinkedList	Design + eviction policy	Hard

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⚙️ Quick Pattern Summary

Pattern	Example Problems	Key Idea
Counting Frequencies	Valid Anagram, Top K Elements	Map for element → count
Prefix Sum	Subarray Sum Equals K	Store sum frequencies
Mapping / Isomorphism	Word Pattern, Isomorphic Strings	One-to-one mapping logic
Sliding Window	Longest Substring Without Repeat	Dynamic map for character indices
Design / System	LRU Cache	Combine Map + LinkedList
Hashing Complex Keys	Group Anagrams, Duplicate Subtrees	Tuples / serialized strings as keys

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💡 Bonus FAANG Map Problems

Problem	Why It’s Important
Minimum Window Substring	Map + sliding window mastery
Alien Dictionary	Map for graph + topological sort
Find All Anagrams in a String	Frequency map + window
Longest Palindrome by Characters	Map counting symmetry
Frequency Sort	Map + custom sorting logic

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🧠 Tips for Mastering Map Problems

1. ✅ Think “mapping” first — whenever you need fast lookups, counts, or relationships.
2. 🧾 Choose the right key — numbers, characters, tuples, or even serialized trees.
3. 💨 Avoid double iteration — most efficient solutions run in O(n) using one map.
4. 🔄 Watch for duplicates or bijection constraints — one-to-one mappings often trap candidates.
5. 🧰 Know built-in Map APIs — putIfAbsent, getOrDefault, computeIfPresent, etc. (Java) or dict.get() (Python).