Problem Solving

Interview-style challenges that combine several ideas.

120 problems

Title	Tags	Acceptance	Difficulty
1. Two Sum	Array · Hash Map	—	Easy
2. Maximum Subarray Sum	Array · Dynamic Programming · Kadane	—	Medium
3. Coin Change	Dynamic Programming	—	Medium
4. Activity Selection	Greedy · Sorting	—	Medium
5. 0/1 Knapsack	Dynamic Programming	—	Hard
6. Merge Intervals	Sorting · Intervals	—	Medium
7. FizzBuzz	Math · Simulation	—	Easy
8. Best Time to Buy and Sell Stock	Array · Greedy	—	Easy
9. Majority Element	Array · Boyer-Moore Voting	—	Easy
10. Move Zeroes	Array · Two Pointers	—	Easy
11. Rotate Array	Array	—	Easy
12. Trapping Rain Water	Two Pointers · Array	—	Hard
13. Product of Array Except Self	Array · Prefix Products	—	Medium
14. Missing Number	Math · Bit Manipulation	—	Easy
15. Range Sum Queries	Prefix Sum	—	Medium
16. Leaders in an Array	Array · Suffix Max	—	Easy
17. Subarrays with Sum K	Prefix Sum · Hash Map	—	Medium
18. Shortest Subarray with Sum ≥ S	Sliding Window · Two Pointers	—	Medium
19. Longest Substring Without Repeats	Sliding Window	—	Medium
20. Longest Run After K Changes	Sliding Window	—	Medium
21. Minimum Window Containing All	Sliding Window	—	Hard
22. Aggressive Cows	Binary Search on Answer	—	Hard
23. Allocate Books	Binary Search on Answer	—	Hard
24. Eating Speed	Binary Search on Answer	—	Medium
25. Triplets with Zero Sum	Two Pointers · Sorting	—	Medium
26. Longest Consecutive Sequence	Hash Set	—	Medium
27. Largest Rectangle in a Histogram	Monotonic Stack	—	Hard
28. The Celebrity	Stack · Elimination	—	Medium
29. Grade Calculator	Conditionals	—	Easy
30. Electricity Bill	Conditionals · Slabs	—	Easy
31. Loan EMI	Formula	—	Medium
32. Day of the Week	Calendar · Zeller	—	Medium
33. Days Between Dates	Calendar	—	Medium
34. 12-Hour to 24-Hour Time	Parsing	—	Easy
35. Seconds to H:M:S	Arithmetic	—	Easy
36. Tic-Tac-Toe Winner	Simulation	—	Easy
37. ATM Withdrawal	Conditionals	—	Easy
38. Parking Fee	Ceil Division	—	Easy
39. Vending Machine Change	Greedy	—	Easy
40. Bank Account Statement	Simulation	—	Medium
41. Library Fine	Conditionals · Dates	—	Easy
42. Password Strength	Validation	—	Easy
43. Validate an IPv4 Address	Parsing · Validation	—	Medium
44. Validate an Email Address	Validation	—	Medium
45. Minesweeper Numbers	Grid	—	Medium
46. Elevator Travel	Simulation	—	Easy
47. Waiting Time at a Counter	Simulation	—	Medium
48. Traffic Light Colour	Modular Arithmetic	—	Easy
49. Word Wrap	Greedy	—	Medium
50. Centre the Text	Formatting	—	Easy
51. Text Histogram	Counting	—	Easy
52. Running Median	Heaps	—	Hard
53. LRU Cache	Design · Linked Hash Map	—	Medium
54. Snakes and Ladders	BFS	—	Hard
55. Bowling Score	Simulation	—	Hard
56. Number to Words	Recursion · Formatting	—	Hard
57. Basic Calculator	Parsing · Stack	—	Hard
58. Inventory Orders	Hash Map · Simulation	—	Medium
59. Rainfall Statistics	Aggregation	—	Easy
60. Cinema Seat Booking	Simulation	—	Medium
61. Temperature Converter	Formula	—	Easy
62. Shopping Cart Total	Arithmetic	—	Easy
63. Robot Moves	Simulation	—	Easy
64. Attendance Shortfall	Math	—	Easy
65. Lottery Matches	Set	—	Easy
66. Reverse a Linked List	Linked List	—	Easy
67. Middle of a Linked List	Two Pointers	—	Easy
68. Remove N-th Node from End	Two Pointers	—	Medium
69. Merge Two Sorted Lists	Linked List · Merge	—	Easy
70. Palindrome Linked List	Two Pointers	—	Easy
71. Remove Duplicates from Sorted List	Linked List	—	Easy
72. Rotate List Right	Linked List	—	Medium
73. Add Two Numbers as Lists	Linked List · Math	—	Medium
74. Partition List	Linked List	—	Medium
75. Odd-Even Linked List	Linked List	—	Medium
76. Swap Nodes in Pairs	Linked List	—	Medium
77. Reverse Nodes in K-Groups	Linked List	—	Hard
78. Container With Most Water	Two Pointers	—	Medium
79. Two Sum II (Sorted Input)	Two Pointers	—	Medium
80. 3Sum Closest	Two Pointers · Sorting	—	Medium
81. Remove Element	Two Pointers	—	Easy
82. Squares of a Sorted Array	Two Pointers	—	Easy
83. Palindrome After One Deletion	Two Pointers	—	Easy
84. Longest Mountain	Two Pointers · DP	—	Medium
85. Windows With Average ≥ Threshold	Sliding Window	—	Medium
86. Max Consecutive Ones With K Flips	Sliding Window	—	Medium
87. Subarray Product Less Than K	Sliding Window	—	Medium
88. Grumpy Bookstore Owner	Sliding Window	—	Medium
89. Maximum Points From Cards	Sliding Window · Prefix Sum	—	Medium
90. Longest Ones After Deleting One Element	Sliding Window	—	Medium
91. Summary Ranges	Array	—	Easy
92. Missing Ranges	Array	—	Easy
93. Sort Array by Parity (Stable)	Array	—	Easy
94. Array Partition (Max Sum of Pair Minimums)	Sorting · Greedy	—	Easy
95. Range Updates With a Difference Array	Prefix Sum	—	Medium
96. Car Pooling	Prefix Sum · Simulation	—	Medium
97. Corporate Flight Bookings	Prefix Sum	—	Medium
98. Kids With the Greatest Number of Candies	Array	—	Easy
99. Shuffle the Array	Array	—	Easy
100. Lemonade Change	Greedy · Simulation	—	Easy
101. Poison Duration	Simulation	—	Easy
102. Can Place Flowers	Greedy	—	Easy
103. Maximum Units on a Truck	Greedy · Sorting	—	Easy
104. Two City Scheduling	Greedy · Sorting	—	Medium
105. Queue Reconstruction by Height	Greedy · Sorting	—	Medium
106. Largest Perimeter Triangle	Sorting · Greedy	—	Easy
107. Custom Sort String	Sorting	—	Medium
108. Add Strings	Math	—	Easy
109. Multiply Strings	Math	—	Medium
110. Compare Version Numbers	Parsing	—	Medium
111. Length of Last Word	String	—	Easy
112. License Key Formatting	String	—	Easy
113. Detect Capital	String	—	Easy
114. Student Attendance Record	String	—	Easy
115. Shortest Distance to a Character	Two Pass	—	Easy
116. Reverse Each Word	String	—	Easy
117. Reverse String II	String	—	Easy
118. Defang an IP Address	String	—	Easy
119. Goal Parser Interpretation	String	—	Easy
120. Nim Game	Game Theory	—	Easy

120 of 120 problems