Pattern 4: Hashing and counting
Comes up in: DSA
This concept is being written. It gets the full five steps — explanation, predict, interview angle, practice with tests, and review cards. Here is exactly what it will cover, so you can study it elsewhere in the meantime.
What it covers
- complement lookup
- frequency maps
- canonical keys (sorted string, count signature)
- sets for O(1) membership
Words you will know
What you will practise
- two-sum (E)
- isomorphic-strings (E)
- majority-element (E)
- group-anagrams (M)
- valid-sudoku (M)
- longest-consecutive-sequence (M)
- top-k-frequent (M)
Interview questions this answers
- Group anagrams efficiently. What key do you use?