Starter 50

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Fifty classic problems that cover every pattern once. The place to begin.

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Tracked companies

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ProblemPatternLevelEvidenceReported

Contains Duplicate
Hashing and countingEasy
Valid Anagram
Hashing and countingEasy
Two Sum
Hashing and countingEasyGrade B
18/25
Group Anagrams
Hashing and countingMediumGrade B
14/25
Valid Palindrome
Two pointersEasyGrade C
7/25
3Sum
Two pointersMediumGrade A
14/25
Container With Most Water
Two pointersMediumGrade B
16/25
Best Time to Buy and Sell Stock
Sliding windowEasyGrade B
17/25
Longest Substring Without Repeating Characters
Sliding windowMediumGrade A
16/25
Longest Repeating Character Replacement
Sliding windowMedium
Valid Parentheses
StackEasyGrade A
16/25
Evaluate Reverse Polish Notation
StackMedium
Binary Search
Binary searchEasy
Find Minimum In Rotated Sorted Array
Binary searchMedium
Search in Rotated Sorted Array
Binary searchMediumGrade A
14/25
Reverse Linked List
Linked listEasyGrade B
10/25
Merge Two Sorted Lists
Linked listEasyGrade B
9/25
Linked List Cycle
Linked listEasyGrade B
4/25
Reorder List
Linked listMedium
Meeting Rooms
IntervalsEasy
Insert Interval
IntervalsMediumGrade C
1/25
Invert Binary Tree
Trees and recursionEasy
Maximum Depth of Binary Tree
Trees and recursionEasyGrade C
4/25
Diameter of Binary Tree
Trees and recursionEasy
Balanced Binary Tree
Trees and recursionEasy
Same Tree
Trees and recursionEasy
Subtree of Another Tree
Trees and recursionEasy
Subsets
BacktrackingMediumGrade C
6/25
Combination Sum
BacktrackingMedium
Word Search
BacktrackingMediumGrade C
7/25
Number of Islands
Graph traversalMediumGrade A
19/25
Clone Graph
Graph traversalMediumGrade C
1/25
Pacific Atlantic Water Flow
Graph traversalMedium
Course Schedule
Topological sortMediumGrade A
15/25
Min Cost to Connect All Points
Shortest pathsMedium
Implement Trie (Prefix Tree)
TrieMediumGrade C
5/25
Kth Largest Element In a Stream
Heap and top-KEasy
Last Stone Weight
Heap and top-KEasy
Jump Game
GreedyMediumGrade A
11/25
Climbing Stairs
Dynamic programmingEasyGrade B
9/25
Min Cost Climbing Stairs
Dynamic programmingEasy
House Robber
Dynamic programmingMediumGrade A
11/25
House Robber II
Dynamic programmingMedium
Unique Paths
Dynamic programmingMedium
Maximum Subarray
Dynamic programmingMediumGrade B
12/25
Number of 1 Bits
Bits and mathEasy
Counting Bits
Bits and mathEasy
Happy Number
Matrix and parsingEasy
Plus One
Matrix and parsingEasy
Min Stack
Design a data structureMediumGrade B
9/25

Evidence shows what candidates commonly report, with the number of tracked companies where it appears. It is not a prediction of what any company will ask.