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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

Ranked by how often each question comes up in real interviews. #1 is the most common.

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🔒