Practice Problems

Each problem teaches a transferable pattern, the kind that shows up again and again in technical interviews at top companies.

150problems

31patterns covered

30+companies represented

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Two Sum

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Free Starter · 5 problems

1.Two Sum
GoogleAmazonMeta
Hash MapEasy
2.Contains Duplicate
AmazonAppleGoogle
SetEasy
3.Valid Anagram
GoogleAmazonMeta
Frequency MapEasy
4.Valid Palindrome
MetaMicrosoftAmazon
Two PointersEasy
5.Valid Parentheses
GoogleAmazonMeta
StackEasy

Premium · 145 problems

Unlock all 145 →

6.Best Time to Buy and Sell Stock
AmazonGoldman SachsGoogle
Tracking MinimumEasy🔒
7.Merge Two Sorted Lists
GoogleAmazonMicrosoft
Linked ListEasy🔒
8.Binary Search
GoogleAmazonMeta
Binary SearchEasy🔒
9.Search Insert Position
GoogleAmazon
Binary SearchEasy🔒
10.Move Zeroes
MetaGoogleAmazon
Two PointersEasy🔒
11.Maximum Subarray
AmazonGoogleApple
Kadane's AlgorithmMedium🔒
12.Longest Substring Without Repeating Characters
AmazonGoogleBloomberg
Sliding WindowMedium🔒
13.Maximum Average Subarray I
AmazonGoogle
Sliding WindowEasy🔒
14.Min Stack
AmazonGoogleBloomberg
StackMedium🔒
15.Invert Binary Tree
GoogleAmazonApple
Tree TraversalEasy🔒
16.Ransom Note
AmazonGoogleMeta
Hash MapEasy🔒
17.Group Anagrams
AmazonGoogleBloomberg
Hash MapMedium🔒
18.Happy Number
AmazonGoogle
SetEasy🔒
19.Longest Consecutive Sequence
GoogleAmazonLinkedIn
SetMedium🔒
20.First Unique Character in a String
AmazonBloombergGoogle
Frequency MapEasy🔒
21.Top K Frequent Elements
AmazonGoogleMeta
Frequency MapMedium🔒
22.Squares of a Sorted Array
GoogleAmazon
Two PointersEasy🔒
23.Two Sum II
AmazonAppleGoogle
Two PointersMedium🔒
24.Minimum Size Subarray Sum
AmazonGoogleMeta
Sliding WindowMedium🔒
25.Permutation in String
AmazonGoogleMicrosoft
Sliding WindowMedium🔒
26.Baseball Game
AmazonGoogle
StackEasy🔒
27.Daily Temperatures
AmazonGoogleMicrosoft
StackMedium🔒
28.First Bad Version
AmazonGoogleMeta
Binary SearchEasy🔒
29.Find Minimum in Rotated Sorted Array
AmazonGoogleMicrosoft
Binary SearchMedium🔒
30.Reverse Linked List
AmazonGoogleApple
Linked ListEasy🔒
31.Linked List Cycle
AmazonGoogleMicrosoft
Linked ListEasy🔒
32.Middle of the Linked List
AmazonGoogle
Linked ListEasy🔒
33.Maximum Product Subarray
AmazonGoogleApple
Kadane's AlgorithmMedium🔒
34.Maximum Depth of Binary Tree
AmazonGoogleMeta
Tree TraversalEasy🔒
35.Same Tree
AmazonGoogle
Tree TraversalEasy🔒
36.Find All Anagrams in a String
AmazonGoogleMicrosoft
Sliding WindowMedium🔒
37.Fruit Into Baskets
AmazonGoogleMeta
Sliding WindowMedium🔒
38.Container With Most Water
GoogleAmazonMeta
Two PointersMedium🔒
39.3Sum
AmazonGoogleMeta
Two PointersMedium🔒
40.Evaluate Reverse Polish Notation
AmazonGoogleLinkedIn
StackMedium🔒
41.Next Greater Element I
AmazonGoogle
StackEasy🔒
42.Next Greater Element II
AmazonGoogle
StackMedium🔒
43.Stock Spanner
AmazonGoogleMicrosoft
StackMedium🔒
44.Largest Rectangle in Histogram
AmazonGoogleMeta
StackHard🔒
45.Search in Rotated Sorted Array
AmazonGoogleMicrosoft
Binary SearchMedium🔒
46.Koko Eating Bananas
AmazonGoogleMeta
Binary SearchMedium🔒
47.Flood Fill
AmazonGoogleMicrosoft
Graph TraversalEasy🔒
48.Number of Islands
AmazonGoogleMeta
Graph TraversalMedium🔒
49.Max Area of Island
AmazonGoogleMeta
Graph TraversalMedium🔒
50.Climbing Stairs
AmazonGoogleApple
Dynamic ProgrammingEasy🔒
51.House Robber
AmazonGoogleMicrosoft
Dynamic ProgrammingMedium🔒
52.Coin Change
AmazonGoogleMeta
Dynamic ProgrammingMedium🔒
53.Subsets
AmazonGoogleMicrosoft
BacktrackingMedium🔒
54.Permutations
GoogleAmazonMicrosoft
BacktrackingMedium🔒
55.Product of Array Except Self
AmazonAppleGoogle
Prefix SumMedium🔒
56.Merge Intervals
GoogleAmazonMeta
IntervalsMedium🔒
57.Missing Number
AmazonGoogleMicrosoft
Bit ManipulationEasy🔒
58.Single Number
AmazonGoogleApple
Bit ManipulationEasy🔒
59.Symmetric Tree
MicrosoftAmazonGoogle
Tree TraversalEasy🔒
60.Binary Tree Level Order Traversal
AmazonGoogleMicrosoft
Tree TraversalMedium🔒
61.Min Cost Climbing Stairs
AmazonGoogle
Dynamic ProgrammingEasy🔒
62.Letter Combinations of a Phone Number
GoogleAmazonMeta
BacktrackingMedium🔒
63.Subarray Sum Equals K
AmazonGoogleMicrosoft
Prefix SumMedium🔒
64.Insert Interval
GoogleAmazonLinkedIn
IntervalsMedium🔒
65.Combinations
GoogleAmazon
BacktrackingMedium🔒
66.Kth Largest Element in an Array
AmazonGoogleMeta
Heap / Priority QueueMedium🔒
67.Word Search
AmazonMicrosoftGoogle
BacktrackingHard🔒
68.Find Median from Data Stream
AmazonGoogleMicrosoft
Two HeapsHard🔒
69.Alien Dictionary
GoogleAmazonMeta
Topological SortHard🔒
70.IPO
Amazon
Two HeapsHard🔒
71.Sliding Window Median
AmazonGoogle
Two HeapsHard🔒
72.Count of Smaller Numbers After Self
GoogleAmazon
Divide and ConquerHard🔒
73.Word Search II
AmazonGoogleMicrosoft
TrieHard🔒
74.Course Schedule
AmazonGoogleMeta
Topological SortMedium🔒
75.Course Schedule II
GoogleAmazonApple
Topological SortMedium🔒
76.Non-Overlapping Intervals
GoogleAmazon
GreedyMedium🔒
77.Clone Graph
AmazonGoogleMeta
Graph TraversalMedium🔒
78.Jump Game
AmazonGoogleMicrosoft
GreedyMedium🔒
79.Jump Game II
AmazonGoogle
GreedyMedium🔒
80.Decode Ways
AmazonGoogleMeta
Dynamic ProgrammingMedium🔒
81.Find the Duplicate Number
AmazonGoogle
Fast and Slow PointersMedium🔒
82.Unique Paths
AmazonGoogleMicrosoft
Dynamic ProgrammingMedium🔒
83.K Closest Points to Origin
AmazonGoogleMeta
Heap / Priority QueueMedium🔒
84.Task Scheduler
AmazonGoogleMicrosoft
GreedyMedium🔒
85.Rotting Oranges
AmazonGoogle
Matrix TraversalMedium🔒
86.Sliding Window Maximum
AmazonGoogleMeta
Monotonic QueueHard🔒
87.Remove Nth Node From End of List
AmazonGoogleMicrosoft
Linked ListMedium🔒
88.Merge K Sorted Lists
AmazonGoogleMicrosoft
K-Way MergeHard🔒
90.Gas Station
AmazonGoogle
GreedyMedium🔒
91.Number of Connected Components in an Undirected Graph
AmazonGoogleLinkedIn
Union-FindMedium🔒
92.First Missing Positive
AmazonGoogleMicrosoft
Cyclic SortHard🔒
93.Sort an Array
GoogleAmazon
Sorting AlgorithmsMedium🔒
94.Range Sum Query - Immutable
AmazonGoogle
Prefix SumEasy🔒
95.Graph Valid Tree
AmazonGoogleLinkedIn
Union-FindMedium🔒
96.Redundant Connection
GoogleAmazon
Union-FindMedium🔒
97.Maximum Sum Circular Subarray
AmazonGoogle
Kadane's AlgorithmMedium🔒
98.Valid Sudoku
AmazonGoogleApple
SetMedium🔒
99.Accounts Merge
GoogleAmazonMeta
Union-FindMedium🔒
100.Word Break
AmazonGoogleMeta
Dynamic ProgrammingMedium🔒
101.Longest Increasing Subsequence
AmazonGoogleMicrosoft
Dynamic ProgrammingMedium🔒
102.Pacific Atlantic Water Flow
GoogleAmazon
Graph TraversalMedium🔒
103.Binary Tree Right Side View
AmazonGoogleMeta
Tree TraversalMedium🔒
104.Balanced Binary Tree
AmazonGoogleMicrosoft
Tree TraversalEasy🔒
105.Construct Binary Tree from Preorder and Inorder Traversal
AmazonGoogleMicrosoft
Tree TraversalMedium🔒
106.Path Sum II
AmazonGoogleMicrosoft
BacktrackingMedium🔒
107.Lowest Common Ancestor of a Binary Tree
AmazonGoogleMeta
Tree TraversalMedium🔒
108.Combination Sum
AmazonGoogleMeta
BacktrackingMedium🔒
109.House Robber II
AmazonGoogle
Dynamic ProgrammingMedium🔒
110.Partition Equal Subset Sum
AmazonGoogle
Dynamic ProgrammingMedium🔒
111.Generate Parentheses
AmazonGoogleMeta
BacktrackingMedium🔒
112.Kth Smallest Element in a BST
AmazonGoogle
Tree TraversalMedium🔒
113.Validate Binary Search Tree
AmazonGoogleBloomberg
Tree TraversalMedium🔒
114.Reverse Bits
AppleAmazon
Bit ManipulationEasy🔒
115.Number of 1 Bits
AppleAmazonGoogle
Bit ManipulationEasy🔒
116.Counting Bits
AmazonGoogle
Bit ManipulationEasy🔒
117.Meeting Rooms
AmazonGoogleMeta
GreedyEasy🔒
118.Meeting Rooms II
AmazonGoogleMeta
GreedyMedium🔒
119.Target Sum
AmazonGoogle
Dynamic ProgrammingMedium🔒
120.Palindrome Partitioning
AmazonGoogle
BacktrackingMedium🔒
121.Longest Palindromic Substring
AmazonGoogleMicrosoft
Two PointersMedium🔒
122.Spiral Matrix
AmazonGoogleMicrosoft
Matrix TraversalMedium🔒
123.Set Matrix Zeroes
AmazonGoogleMicrosoft
Matrix TraversalMedium🔒
124.Search a 2D Matrix
AmazonGoogleMicrosoft
Binary SearchMedium🔒
125.Add Two Numbers
AmazonGoogleMicrosoft
Linked ListMedium🔒
126.Reorder List
AmazonGoogle
Linked ListMedium🔒
127.Number of Provinces
AmazonGoogle
Graph TraversalMedium🔒
128.Keys and Rooms
AmazonGoogle
Graph TraversalMedium🔒
129.Find Peak Element
GoogleAmazonMeta
Binary SearchMedium🔒
130.Edit Distance
AmazonGoogleMicrosoft
Dynamic ProgrammingHard🔒
131.Running Sum of 1d Array
AmazonGoogle
Prefix SumEasy🔒
132.Find All Numbers Disappeared in an Array
AmazonGoogle
Cyclic SortEasy🔒
133.Intersection of Two Arrays
AmazonGoogleMicrosoft
SetEasy🔒
134.Jump Game VI
AmazonGoogle
Monotonic QueueMedium🔒
135.Find K Pairs with Smallest Sums
AmazonGoogleMicrosoft
Heap / Priority QueueMedium🔒
136.Minimum Window Substring
AmazonGoogleMeta
Sliding WindowHard🔒
137.Trapping Rain Water
AmazonGoogleMeta
Two PointersHard🔒
138.Implement Trie (Prefix Tree)
AmazonGoogleMicrosoft
TrieMedium🔒
139.Best Time to Buy and Sell Stock II
AmazonGoogle
GreedyEasy🔒
140.Find Pivot Index
AmazonGoogle
Prefix SumEasy🔒
141.Word Break II
AmazonGoogle
MemoizationHard🔒
142.Number of Islands II
GoogleAmazonMicrosoft
Union-FindHard🔒
143.Maximum Difference Between Increasing Elements
AmazonGoogle
Tracking MinimumEasy🔒
144.Minimum Path Sum
AmazonGoogleMicrosoft
Dynamic ProgrammingMedium🔒
145.Longest Common Subsequence
AmazonGoogleMicrosoft
Dynamic ProgrammingMedium🔒
146.Maximum Product of Word Lengths
AmazonGoogle
Bit ManipulationMedium🔒
147.Single Number II
AmazonGoogle
Bit ManipulationMedium🔒
148.Rotate Image
AmazonGoogleMicrosoft
Matrix TraversalMedium🔒
149.Surrounded Regions
AmazonGoogleMicrosoft
Graph TraversalMedium🔒
150.Decode String
GoogleAmazonMicrosoft
StackMedium🔒
151.Find All Duplicates in an Array
AmazonGoogle
Cyclic SortMedium🔒

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