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LeetCode problem approaches

The key insight, optimal strategy, and complexity for the problems that come up most — then generate an interactive lesson to see each one run step by step.

Easy(13)

Two SumHashing & Frequency Maps
Easy
Contains DuplicateHashing & Frequency Maps
Easy
Valid AnagramHashing & Frequency Maps
Easy
Valid PalindromeTwo Pointers
Easy
Best Time to Buy and Sell StockSliding Window
Easy
Valid Parentheses
Easy
Binary SearchBinary Search
Easy
Reverse Linked List
Easy
Merge Two Sorted Lists
Easy
Linked List CycleFast & Slow Pointers
Easy
Invert Binary TreeGraph Traversal (BFS & DFS)
Easy
Maximum Depth of Binary TreeGraph Traversal (BFS & DFS)
Easy
Climbing StairsDynamic Programming
Easy

Medium(31)

Group AnagramsHashing & Frequency Maps
Medium
Top K Frequent ElementsHeap / Priority QueueHashing & Frequency Maps
Medium
Product of Array Except SelfPrefix Sums
Medium
Longest Consecutive SequenceHashing & Frequency Maps
Medium
Two Sum II - Input Array Is SortedTwo Pointers
Medium
3SumTwo Pointers
Medium
Container With Most WaterTwo Pointers
Medium
Longest Substring Without Repeating CharactersSliding WindowHashing & Frequency Maps
Medium
Longest Repeating Character ReplacementSliding Window
Medium
Min Stack
Medium
Daily TemperaturesMonotonic Stack
Medium
Search in Rotated Sorted ArrayBinary Search
Medium
Find Minimum in Rotated Sorted ArrayBinary Search
Medium
Koko Eating BananasBinary Search
Medium
Find the Duplicate NumberFast & Slow Pointers
Medium
Binary Tree Level Order TraversalGraph Traversal (BFS & DFS)
Medium
Number of IslandsGraph Traversal (BFS & DFS)Union-Find (Disjoint Set)
Medium
Clone GraphGraph Traversal (BFS & DFS)
Medium
Course ScheduleTopological SortGraph Traversal (BFS & DFS)
Medium
House RobberDynamic Programming
Medium
Coin ChangeDynamic Programming
Medium
Longest Increasing SubsequenceDynamic ProgrammingBinary Search
Medium
Word BreakDynamic Programming
Medium
SubsetsBacktracking
Medium
Combination SumBacktracking
Medium
PermutationsBacktracking
Medium
Merge IntervalsIntervals
Medium
Meeting Rooms IIIntervalsHeap / Priority Queue
Medium
Kth Largest Element in an ArrayHeap / Priority Queue
Medium
Subarray Sum Equals KPrefix SumsHashing & Frequency Maps
Medium
Maximum SubarrayDynamic Programming
Medium

Hard(4)

Trapping Rain WaterTwo PointersMonotonic Stack
Hard
Minimum Window SubstringSliding Window
Hard
Largest Rectangle in HistogramMonotonic Stack
Hard
Find Median from Data StreamHeap / Priority Queue
Hard