Tree
66 problems · 57 with full explanations
15 Easy38 Medium3 Hard
Tree problems typically require recursive DFS or iterative BFS. Common patterns: preorder for serialization, inorder for BST sorted output, postorder for bottom-up aggregation. Always consider edge cases: null nodes, single-node trees, and skewed (list-like) trees.
How to practice
To practice Tree problems effectively, start with the Easy problems listed below, trace through each solution on paper, then re-implement without looking. When you can recognise the tree pattern within 30 seconds of reading a new problem, move on to Medium difficulty. Use the related topic pages and our study guide for a structured progression.
Start here (Easy + explained)
All Tree problems
- 99.Recover Binary Search TreeMedium
- 100.Same TreeEasy
- 102.Binary Tree Level Order TraversalMedium
- 106.Construct Binary Tree from Inorder and Postorder TraversalMedium
- 107.Binary Tree Level Order Traversal IIMedium
- 108.Convert Sorted Array to Binary Search TreeEasy
- 110.Balanced Binary TreeEasy
- 111.Minimum Depth of Binary TreeEasy
- 112.Path SumEasy
- 113.Path Sum IIMedium
- 114.Flatten Binary Tree to Linked ListMedium
- 144.Binary Tree Preorder TraversalEasy
- 145.Binary Tree Postorder TraversalEasy
- 222.Count Complete Tree NodesMedium
- 230.Kth Smallest Element in a BSTMedium
- 236.Lowest Common Ancestor of a Binary TreeMedium
- 257.Binary Tree PathsEasy
- 331.Verify Preorder Serialization of a Binary TreeUnknown
- 429.N-ary Tree Level Order TraversalMedium
- 508.Most Frequent Subtree SumMedium
- 513.Find Bottom Left Tree ValueMedium
- 515.Find Largest Value in Each Tree RowMedium
- 558.Logical OR of Two Binary Grids Represented as Quad-TreesUnknown
- 590.N-ary Tree Postorder TraversalEasy
- 623.Add One Row to TreeMedium
- 700.Search in a Binary Search TreeEasy
- 703.Kth Largest Element in a StreamEasy
- 834.Sum of Distances in TreeUnknown
- 865.Smallest Subtree with all the Deepest NodesMedium
- 889.Construct Binary Tree from Preorder and Postorder TraversalMedium
- 951.Flip Equivalent Binary TreesMedium
- 965.Univalued Binary TreeEasy
- 998.Maximum Binary Tree IIMedium
- 1022.Sum of Root To Leaf Binary NumbersEasy
- 1028.Recover a Tree From Preorder TraversalHard
- 1038.Binary Search Tree to Greater Sum TreeMedium
- 1080.Insufficient Nodes in Root to Leaf PathsMedium
- 1110.Delete Nodes And Return ForestMedium
- 1123.Lowest Common Ancestor of Deepest LeavesMedium
- 1161.Maximum Level Sum of a Binary TreeMedium
- 1261.Find Elements in a Contaminated Binary TreeMedium
- 1305.All Elements in Two Binary Search TreesUnknown
- 1339.Maximum Product of Splitted Binary TreeMedium
- 1367.Linked List in Binary TreeMedium
- 1382.Balance a Binary Search TreeMedium
- 1530.Number of Good Leaf Nodes PairsMedium
- 1766.Tree of CoprimesUnknown
- 1938.Maximum Genetic Difference QueryUnknown
- 2096.Step-By-Step Directions From a Binary Tree Node to AnotherMedium
- 2196.Create Binary Tree From DescriptionsMedium
- 2236.Root Equals Sum of ChildrenEasy
- 2322.Minimum Score After Removals on a TreeUnknown
- 2331.Evaluate Boolean Binary TreeEasy
- 2415.Reverse Odd Levels of Binary TreeMedium
- 2440.Create Components With Same ValueMedium
- 2458.Height of Binary Tree After Subtree Removal QueriesUnknown
- 2467.Most Profitable Path in a TreeMedium
- 2471.Minimum Number of Operations to Sort a Binary Tree by LevelHard
- 2509.Cycle Length Queries in a TreeMedium
- 2583.Kth Largest Sum in a Binary TreeMedium
- 2641.Cousins in Binary Tree IIMedium
- 2872.Maximum Number of K-Divisible ComponentsUnknown
- 3068.Find the Maximum Sum of Node ValuesHard
- 3203.Find Minimum Diameter After Merging Two TreesMedium
- 3372.Maximize the Number of Target Nodes After Connecting Trees IMedium
- 3373.Maximize the Number of Target Nodes After Connecting Trees IIUnknown