Breadth-First Search
56 problems · 39 with full explanations
3 Easy26 Medium13 Hard
BFS explores nodes level by level, guaranteeing the shortest path in unweighted graphs. Use a Queue<T> and a visited set. Classic applications: shortest path, level-order tree traversal, multi-source distance (e.g., "01 matrix"), and word ladder transformations.
How to practice
To practice Breadth-First Search 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 breadth-first search 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 Breadth-First Search problems
- 102.Binary Tree Level Order TraversalMedium
- 107.Binary Tree Level Order Traversal IIMedium
- 111.Minimum Depth of Binary TreeEasy
- 126.Word Ladder IIHard
- 210.Course Schedule IIMedium
- 310.Minimum Height TreesUnknown
- 329.Longest Increasing Path in a MatrixHard
- 407.Trapping Rain Water IIHard
- 417.Pacific Atlantic Water FlowMedium
- 429.N-ary Tree Level Order TraversalMedium
- 513.Find Bottom Left Tree ValueMedium
- 515.Find Largest Value in Each Tree RowMedium
- 623.Add One Row to TreeMedium
- 684.Redundant ConnectionMedium
- 752.Open the LockMedium
- 756.Pyramid Transition MatrixUnknown
- 773.Sliding PuzzleHard
- 778.Swim in Rising WaterHard
- 802.Find Eventual Safe StatesMedium
- 827.Making A Large IslandHard
- 839.Similar String GroupsHard
- 851.Loud and RichMedium
- 909.Snakes and LaddersMedium
- 928.Minimize Malware Spread IIUnknown
- 959.Regions Cut By SlashesUnknown
- 965.Univalued Binary TreeEasy
- 1123.Lowest Common Ancestor of Deepest LeavesMedium
- 1161.Maximum Level Sum of a Binary TreeMedium
- 1261.Find Elements in a Contaminated Binary TreeMedium
- 1298.Maximum Candies You Can Get from BoxesUnknown
- 1319.Number of Operations to Make Network ConnectedMedium
- 1368.Minimum Cost to Make at Least One Valid Path in a GridHard
- 1462.Course Schedule IVMedium
- 1568.Minimum Number of Days to Disconnect IslandUnknown
- 1625.Lexicographically Smallest String After Applying OperationsUnknown
- 1765.Map of Highest PeakMedium
- 1905.Count Sub IslandsUnknown
- 1970.Last Day Where You Can Still CrossUnknown
- 1971.Find if Path Exists in GraphEasy
- 2045.Second Minimum Time to Reach DestinationUnknown
- 2092.Find All People With SecretUnknown
- 2115.Find All Possible Recipes from Given SuppliesUnknown
- 2192.All Ancestors of a Node in a Directed Acyclic GraphMedium
- 2290.Minimum Obstacle Removal to Reach CornerHard
- 2471.Minimum Number of Operations to Sort a Binary Tree by LevelHard
- 2493.Divide Nodes Into the Maximum Number of GroupsHard
- 2503.Maximum Number of Points From Grid QueriesHard
- 2577.Minimum Time to Visit a Cell In a GridHard
- 2583.Kth Largest Sum in a Binary TreeMedium
- 2641.Cousins in Binary Tree IIMedium
- 2658.Maximum Number of Fish in a GridMedium
- 2685.Count the Number of Complete ComponentsMedium
- 3203.Find Minimum Diameter After Merging Two TreesMedium
- 3243.Shortest Distance After Road Addition Queries IUnknown
- 3372.Maximize the Number of Target Nodes After Connecting Trees IMedium
- 3373.Maximize the Number of Target Nodes After Connecting Trees IIUnknown