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🌳 Interview Prep

Trees, Graphs & DP

Trees, heaps, tries, graphs, backtracking and dynamic programming: what separates a pass from a strong pass at big tech.

📘 Learn it from scratch

Visual, hands-on lessons for every pattern in this topic. Do the lesson, then come back and the questions click.

Trees & Binary Search TreesTree TraversalsBinary Search Trees in DepthHeaps & Priority QueuesTries (Prefix Trees)Graphs: BFS & DFSGrids & Matrix TraversalDynamic Programming, DemystifiedRecursion, Step by Step

100 questions, most asked first

Ordered so the most useful questions for learning each pattern come first.

Any difficulty Easy Medium Hard

All patterns Tree DFS Tree BFS BST Grid graph 1D DP Heap Graph BFS/DFS Topological sort Backtracking 2D DP Trie Union-find Shortest path Recursion

#1Maximum Depth of Binary TreeTree DFSEasyFree #2Invert Binary TreeTree DFSEasyFree #3Same TreeTree DFSEasyFree #4Binary Tree Level Order TraversalTree BFSMediumFree #5Validate Binary Search TreeBSTMediumFree #6Lowest Common Ancestor of a BSTBSTMediumFree #7Number of IslandsGrid graphMediumFree #8Climbing Stairs1D DPEasyFree #9Coin Change1D DPMediumFree #10Kth Largest Element in an ArrayHeapMediumFree Unlock 90 more Trees, Graphs & DP questions · all 1,200 questions for $39/year (about 11¢ a day)See full access #11Subtree of Another TreeTree DFSEasy🔒#12Diameter of Binary TreeTree DFSEasy🔒#13Balanced Binary TreeTree DFSEasy🔒#14Binary Tree Right Side ViewTree BFSMedium🔒#15Kth Smallest Element in a BSTBSTMedium🔒#16Construct Binary Tree from Preorder and InorderTree DFSMedium🔒#17Serialize and Deserialize Binary TreeTree BFSHard🔒#18Binary Tree Maximum Path SumTree DFSHard🔒#19Lowest Common Ancestor of a Binary TreeTree DFSMedium🔒#20Clone GraphGraph BFS/DFSMedium🔒#21Course ScheduleTopological sortMedium🔒#22Course Schedule IITopological sortMedium🔒#23Pacific Atlantic Water FlowGrid graphMedium🔒#24Rotting OrangesGrid graphMedium🔒#25Max Area of IslandGrid graphMedium🔒#26Word SearchBacktrackingMedium🔒#27SubsetsBacktrackingMedium🔒#28PermutationsBacktrackingMedium🔒#29Combination SumBacktrackingMedium🔒#30Generate ParenthesesBacktrackingMedium🔒#31House Robber1D DPMedium🔒#32House Robber II1D DPMedium🔒#33Longest Increasing Subsequence1D DPMedium🔒#34Word Break1D DPMedium🔒#35Decode Ways1D DPMedium🔒#36Unique Paths2D DPMedium🔒#37Longest Common Subsequence2D DPMedium🔒#38Edit Distance2D DPMedium🔒#39Longest Palindromic Substring2D DPMedium🔒#40Palindromic Substrings2D DPMedium🔒#41Implement Trie (Prefix Tree)TrieMedium🔒#42Design Add and Search WordsTrieMedium🔒#43Word Search IITrieHard🔒#44Find Median from Data StreamHeapHard🔒#45K Closest Points to OriginHeapMedium🔒#46Last Stone WeightHeapEasy🔒#47Task SchedulerHeapMedium🔒#48Number of Connected Components in a GraphUnion-findMedium🔒#49Graph Valid TreeUnion-findMedium🔒#50Redundant ConnectionUnion-findMedium🔒#51Network Delay TimeShortest pathMedium🔒#52Cheapest Flights Within K StopsShortest pathMedium🔒#53Word LadderGraph BFS/DFSHard🔒#54Alien DictionaryTopological sortHard🔒#55Surrounded RegionsGrid graphMedium🔒#56Shortest Path in Binary MatrixGrid graphMedium🔒#57N-QueensBacktrackingHard🔒#58Letter Combinations of a Phone NumberBacktrackingMedium🔒#59Combination Sum IIBacktrackingMedium🔒#60Subsets IIBacktrackingMedium🔒#61Palindrome PartitioningBacktrackingMedium🔒#62Min Cost Climbing Stairs1D DPEasy🔒#63Maximum Product Subarray1D DPMedium🔒#64Partition Equal Subset Sum1D DPMedium🔒#65Coin Change II1D DPMedium🔒#66Target Sum1D DPMedium🔒#67Minimum Path Sum2D DPMedium🔒#68Longest Increasing Path in a Matrix2D DPHard🔒#69Interleaving String2D DPMedium🔒#70Best Time to Buy and Sell Stock with Cooldown2D DPMedium🔒#71Maximal Square2D DPMedium🔒#72Binary Tree Inorder Traversal (Iterative)Tree DFSEasy🔒#73Symmetric TreeTree DFSEasy🔒#74Path SumTree DFSEasy🔒#75Path Sum IIBacktrackingMedium🔒#76Count Good Nodes in Binary TreeTree DFSMedium🔒#77Convert Sorted Array to Balanced BSTBSTEasy🔒#78Delete Node in a BSTBSTMedium🔒#79Insert into a BSTBSTMedium🔒#80Binary Tree Zigzag Level Order TraversalTree BFSMedium🔒#81Average of Levels in Binary TreeTree BFSEasy🔒#82Minimum Depth of Binary TreeTree BFSEasy🔒#83Flatten Binary Tree to Linked ListTree DFSMedium🔒#84Sum Root to Leaf NumbersTree DFSMedium🔒#85All Nodes Distance K in Binary TreeGraph BFS/DFSMedium🔒#86Is Graph Bipartite?Graph BFS/DFSMedium🔒#87Keys and RoomsGraph BFS/DFSMedium🔒#88Find the Town JudgeGraph BFS/DFSEasy🔒#89Evaluate DivisionGraph BFS/DFSMedium🔒#90Accounts MergeUnion-findMedium🔒#91Jump Game II1D DPMedium🔒#92Min Cost to Connect All PointsUnion-findMedium🔒#93Swim in Rising WaterShortest pathHard🔒#94Path With Minimum EffortShortest pathMedium🔒#95Fibonacci Number (Recursion → Memo → DP)RecursionEasy🔒#96Letter Case PermutationBacktrackingMedium🔒#97Burst Balloons2D DPHard🔒#98Regular Expression Matching2D DPHard🔒#99Reconstruct ItineraryGraph BFS/DFSHard🔒#100Unique Binary Search Trees1D DPMedium🔒