Hashing

Counting, grouping and fast lookups with maps and sets.

64 problems

Title	Tags	Acceptance	Difficulty
1. Missing and Repeating	Array · Math	—	Medium
2. Pair with Given Difference	Hash Set	—	Medium
3. Count Pairs with Sum	Hash Map · Counting	—	Medium
4. Subarrays with Sum K	Prefix Sum · Hash Map	—	Medium
5. Longest Subarray with Sum K	Prefix Sum · Hash Map	—	Medium
6. Elements More Than n/3 Times	Counting	—	Medium
7. Intersection of Two Arrays	Set	—	Easy
8. Union of Two Arrays	Set	—	Easy
9. Sort by Frequency	Sorting · Hash Map	—	Medium
10. First Repeating Element	Hash Map	—	Easy
11. Distinct Elements in Every Window	Sliding Window · Hash Map	—	Medium
12. Character Frequency	Hash Map	—	Easy
13. Isogram Check	Set	—	Easy
14. Pangram Check	Set	—	Easy
15. First Non-Repeating Character Index	Hash Map	—	Easy
16. Longest Substring Without Repeats	Sliding Window	—	Medium
17. Count Anagram Groups	Hash Map · Sorting	—	Medium
18. Most Frequent Character	Counting	—	Easy
19. Word Pattern	Hash Map · Bijection	—	Easy
20. Isomorphic Strings	Hash Map	—	Easy
21. Make Anagrams	Counting	—	Easy
22. Minimum Window Containing All	Sliding Window	—	Hard
23. Happy Number	Cycle Detection	—	Easy
24. Contains Duplicate	Hash Set	—	Easy
25. Nearby Duplicate	Hash Map · Sliding Window	—	Easy
26. Longest Consecutive Sequence	Hash Set	—	Medium
27. Top K Frequent Words	Hash Map · Sorting	—	Medium
28. Valid Sudoku	Hash Set	—	Medium
29. Zero-Sum Subarray Exists?	Prefix Sum · Hash Set	—	Easy
30. Count Distinct Values	Hash Set	—	Easy
31. Four Arrays Zero Sum	Hash Map · Meet in the Middle	—	Medium
32. Pairs with Equal Digit Sum	Hash Map	—	Medium
33. Distinct Pairs with Sum	Hash Set	—	Medium
34. First Unique After Each Step	Queue · Hash Map	—	Medium
35. Text Histogram	Counting	—	Easy
36. LRU Cache	Design · Linked Hash Map	—	Medium
37. Inventory Orders	Hash Map · Simulation	—	Medium
38. Lottery Matches	Set	—	Easy
39. Fruit Into Baskets	Sliding Window · Hash Map	—	Medium
40. Subarrays With Exactly K Odd Numbers	Prefix Sum · Hash Map	—	Medium
41. Binary Subarrays With Sum	Prefix Sum	—	Medium
42. Longest Substring With K Distinct Characters	Sliding Window	—	Medium
43. Permutation in String	Sliding Window	—	Medium
44. Find All Anagrams in a String	Sliding Window	—	Medium
45. Subarray Sums Divisible by K	Prefix Sum · Modulo	—	Medium
46. Longest Equal 0s and 1s	Prefix Sum · Hash Map	—	Medium
47. Find All Duplicates	Array	—	Medium
48. First Missing Positive	Array · Cyclic Sort	—	Hard
49. Find All Missing Numbers	Array	—	Easy
50. Relative Sort Array	Counting Sort	—	Easy
51. Longest Harmonious Subsequence	Hash Map	—	Easy
52. Degree of an Array	Hash Map	—	Easy
53. Number of Good Pairs	Counting	—	Easy
54. How Many Numbers Are Smaller	Counting Sort	—	Easy
55. Distribute Candies	Hash Set	—	Easy
56. Ransom Note	Counting	—	Easy
57. Jewels and Stones	Hash Set	—	Easy
58. Uncommon Words From Two Sentences	Hash Map	—	Easy
59. Longest Palindrome You Can Build	Counting	—	Easy
60. Determine if Two Strings Are Close	Counting	—	Medium
61. Maximum Number of Balloons	Counting	—	Easy
62. Bulls and Cows	Counting	—	Medium
63. Find the Difference	Bit Manipulation · Counting	—	Easy
64. Count Consistent Strings	Hash Set	—	Easy

64 of 64 problems