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Hashing & Maps — Complete Guide (Problems 161–205)
Master HashMap, HashSet, and cache design patterns with 45 problems, 5-language solutions, and MAANG company tags.
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Two Sum [Easy] — HashMap Complement Lookup
Find two indices that add to target in O(n) by storing each number in a HashMap and looking up the complement.
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Valid Anagram [Easy] — Frequency Counter
Check if two strings are anagrams by comparing their character frequency counts using an array or HashMap.
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Ransom Note [Easy] — Frequency Map Check
Check if a ransom note can be constructed from magazine letters using a character frequency map.
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Isomorphic Strings [Easy] — Two-Way Character Mapping
Check if two strings are isomorphic by maintaining bidirectional character mappings to ensure a consistent one-to-one correspondence.
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