You've learned the core hash map patterns. Two Sum taught you complement checking: for each element, check if its partner exists. Contains Duplicate showed basic set usage for tracking seen elements. Group Anagrams demonstrated using computed keys for grouping: transform elements to a canonical form and group by that form. Product Except Self revealed the prefix/suffix pattern: precompute cumulative values from both directions. These patterns appear constantly. When you see "find pairs," think hash map. When you see "group similar items," compute a key. When you see "combine info from left and right," think prefix/suffix. Next section: Two Pointers.
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$ curl repovive.com/roadmaps/maang-interview-prep/arrays-hashing/section-recap
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