Solutions

Merge Two Sorted Lists Easy Linked List Cycle Easy Palindrome Linked List Easy Remove Linked List Elements Easy Remove Duplicates From Sorted List Easy Middle of the Linked List Easy Intersection of Two Linked Lists Easy Merge in Between Linked Lists Medium Merge Nodes in Between Zeros Medium Find the Minimum and Maximum Number of Nodes Between Critical Points Medium Remove Nodes From Linked List Medium Reorder List Medium Maximum Twin Sum Of A Linked List Medium Remove Nth Node From End of List Medium Delete Nodes From Linked List Present in Array Medium Swapping Nodes in a Linked List Medium Copy List With Random Pointer Medium Design Linked List Medium Design Browser History Medium Add Two Numbers Medium Find The Duplicate Number Medium Swap Nodes In Pairs Medium Sort List Medium Partition List Medium Rotate List Medium Reverse Linked List II Medium Design Circular Queue Medium Insertion Sort List Medium Split Linked List in Parts Medium LRU Cache Medium LFU Cache Hard Merge K Sorted Lists Hard Reverse Nodes In K Group Hard

Trees

Binary Tree Inorder Traversal Easy Binary Tree Preorder Traversal Easy Binary Tree Postorder Traversal Easy N-ary Tree Postorder Traversal Easy Invert Binary Tree Easy Maximum Depth of Binary Tree Easy Diameter of Binary Tree Easy Balanced Binary Tree Easy Same Tree Easy Subtree of Another Tree Easy Convert Sorted Array to Binary Search Tree Easy Merge Two Binary Trees Easy Path Sum Easy Range Sum of BST Easy Leaf-Similar Trees Easy Evaluate Boolean Binary Tree Easy Create Binary Tree From Descriptions Medium Populating Next Right Pointers In Each Node Medium Binary Tree Vertical Order Traversal Medium Construct String From Binary Tree Medium Lowest Common Ancestor of a Binary Search Tree Medium Insert into a Binary Search Tree Medium Delete Node in a BST Medium Binary Tree Level Order Traversal Medium Binary Tree Right Side View Medium Reverse Odd Levels of Binary Tree Medium Minimum Number of Operations to Sort a Binary Tree by Level Medium Kth Largest Sum in a Binary Tree Medium Cousins in Binary Tree II Medium Minimum Distance between BST Nodes Easy Symmetric Tree Easy Linked List in Binary Tree Medium Minimum Time to Collect All Apples in a Tree Medium Binary Tree Zigzag Level Order Traversal Medium Construct Quad Tree Medium Find Duplicate Subtrees Medium Check Completeness of a Binary Tree Medium Construct Binary Tree from Inorder and Postorder Traversal Medium Maximum Width of Binary Tree Medium Time Needed to Inform All Employees Medium Count Good Nodes In Binary Tree Medium Validate Binary Search Tree Medium Kth Smallest Element In a Bst Medium Construct Binary Tree From Preorder And Inorder Traversal Medium Construct Binary Tree from Preorder and Postorder Traversal Medium Unique Binary Search Trees Medium Unique Binary Search Trees II Medium Number of Good Leaf Nodes Pairs Medium Sum Root to Leaf Numbers Medium House Robber III Medium Flip Equivalent Binary Trees Medium Operations On Tree Medium All Possible Full Binary Trees Medium Find Bottom Left Tree Value Medium Trim a Binary Search Tree Medium Binary Search Tree Iterator Medium Validate Binary Tree Nodes Medium Find Largest Value in Tree Row Medium Pseudo-Palindromic Paths in a Binary Tree Medium Even Odd Tree Medium Smallest String Starting From Leaf Medium Delete Leaves With a Given Value Medium Delete Nodes And Return Forest Medium Distribute Coins in Binary Tree Medium Convert Bst to Greater Tree Medium Step-By-Step Directions From a Binary Tree Node to Another Medium Recover a Tree From Preorder Traversal Hard Binary Tree Maximum Path Sum Hard Serialize And Deserialize Binary Tree Hard

Heap / Priority Queue

Kth Largest Element In a Stream Easy Last Stone Weight Easy Take Gifts From the Richest Pile Easy Final Array State After K Multiplication Operations I Easy K Closest Points to Origin Medium Kth Largest Element In An Array Medium Task Scheduler Medium Design Twitter Medium Least Number of Unique Integers after K Removal Medium Furthest Building You Can Reach Medium Minimize Deviation in Array Hard Maximum Subsequence Score Medium Single Threaded CPU Medium Seat Reservation Manager Medium Process Tasks Using Servers Medium Find The Kth Largest Integer In The Array Medium Reorganize String Medium Longest Happy String Medium Car Pooling Medium Range Sum of Sorted Subarray Sums Medium Find Median From Data Stream Hard Maximum Performance of a Team Hard IPO Hard Minimum Cost to Hire K Workers Hard Number of Flowers in Full Bloom Hard Constrained Subsequence Sum Hard Find Building Where Alice and Bob Can Meet Hard

Backtracking

Sum of All Subsets XOR Total Easy Subsets Medium Combination Sum Medium Combination Sum II Medium Combinations Medium Permutations Medium Subsets II Medium Permutations II Medium Generate Parentheses Medium Letter Tile Possibilities Medium Word Search Medium Palindrome Partitioning Medium Restore IP Addresses Medium Letter Combinations of a Phone Number Medium The k-th Lexicographical String of All Happy Strings of Length n Medium Matchsticks to Square Medium Splitting a String Into Descending Consecutive Values Medium Construct Smallest Number From DI String Medium Find Unique Binary String Medium Split a String Into the Max Number of Unique Substrings Medium Maximum Length of a Concatenated String With Unique Characters Medium Partition to K Equal Sum Subsets Medium The Number of Beautiful Subsets Medium Different Ways to Add Parentheses Medium Construct the Lexicographically Largest Valid Sequence Medium Count Number of Maximum Bitwise-OR Subsets Medium N Queens Hard N Queens II Hard Maximum Score Words Formed By Letters Hard Word Break II Hard

Tries

Count Prefix and Suffix Pairs I Easy Implement Trie Prefix Tree Medium Design Add And Search Words Data Structure Medium Counting Words With a Given Prefix Easy Remove Sub-Folders from the Filesystem Medium Extra Characters in a String Medium Word Search II Hard Sum of Prefix Scores of Strings Hard Count Prefix and Suffix Pairs II Hard

Graphs

Island Perimeter Easy Verifying An Alien Dictionary Easy Find the Town Judge Easy Count Servers that Communicate Medium Find Champion II Medium Number of Islands Medium Max Area of Island Medium Maximum Number of Fish in a Grid Medium Clone Graph Medium Walls And Gates Medium Rotting Oranges Medium Count Sub Islands Medium Pacific Atlantic Water Flow Medium Surrounded Regions Medium Reorder Routes to Make All Paths Lead to The City Zero Medium Snakes And Ladders Medium Open The Lock Medium Find Eventual Safe States Medium Course Schedule Medium Course Schedule II Medium Graph Valid Tree Medium Course Schedule IV Medium Check if Move Is Legal Medium Shortest Bridge Medium Shortest Path in Binary Matrix Medium Number of Connected Components In An Undirected Graph Medium Redundant Connection Medium

1028. Recover a Tree From Preorder Traversal - Explanation

Links

Blind 75
NeetCode 150
NeetCode 250
How to use NeetCode Effectively
System Design

Social

YouTube
LinkedIn
Twitter

Contact

support@neetcode.io

Legal

Privacy Policy
Terms of Service

Copyright © 2026 neetcode.io All rights reserved.