Breadth-First Search LeetCode Problems: All 223, With Python Solutions
Every problem in this library that LeetCode tags Breadth-First Search — 223 in total, 178 of them with a complete Python solution, a worked example and the time and space complexity of the approach.
- 223 problems
- 20 Easy
- 142 Medium
- 61 Hard
How Breadth-First Search problems are solved
A tag names the subject, not the method. These pattern hubs cover the techniques that actually solve Breadth-First Search problems — each one explains the approach, gives a Python template and states its complexity.
- Breadth-First Search — Expand outward level by level, so the first time you arrive is the shortest way.
Breadth-First Search problems by difficulty
Showing the first 200 of 223 problems. Problems with a complete Python solution are listed first, then by ascending problem number.
Easy (19)
| # | Problem | Difficulty | Topics |
|---|---|---|---|
| 100 | Same Tree | Easy | Tree, Depth-First Search, Breadth-First Search +1 |
| 101 | Symmetric Tree | Easy | Tree, Depth-First Search, Breadth-First Search +1 |
| 104 | Maximum Depth of Binary Tree | Easy | Tree, Depth-First Search, Breadth-First Search +1 |
| 111 | Minimum Depth of Binary Tree | Easy | Tree, Depth-First Search, Breadth-First Search +1 |
| 112 | Path Sum | Easy | Tree, Depth-First Search, Breadth-First Search +1 |
| 226 | Invert Binary Tree | Easy | Tree, Depth-First Search, Breadth-First Search +1 |
| 404 | Sum of Left Leaves | Easy | Tree, Depth-First Search, Breadth-First Search +1 |
| 463 | Island Perimeter | Easy | Depth-First Search, Breadth-First Search, Array +1 |
| 530 | Minimum Absolute Difference in BST | Easy | Tree, Depth-First Search, Breadth-First Search +2 |
| 559 | Maximum Depth of N-ary Tree | Easy | Tree, Depth-First Search, Breadth-First Search |
| 617 | Merge Two Binary Trees | Easy | Tree, Depth-First Search, Breadth-First Search +1 |
| 637 | Average of Levels in Binary Tree | Easy | Tree, Depth-First Search, Breadth-First Search +1 |
| 653 | Two Sum IV - Input is a BST | Easy | Tree, Depth-First Search, Breadth-First Search +4 |
| 733 | Flood Fill | Easy | Depth-First Search, Breadth-First Search, Array +1 |
| 783 | Minimum Distance Between BST Nodes | Easy | Tree, Depth-First Search, Breadth-First Search +2 |
| 965 | Univalued Binary Tree | Easy | Tree, Depth-First Search, Breadth-First Search +1 |
| 993 | Cousins in Binary Tree | Easy | Tree, Depth-First Search, Breadth-First Search +1 |
| 1379 | Find a Corresponding Node of a Binary Tree in a Clone of That Tree | Easy | Tree, Depth-First Search, Breadth-First Search +1 |
| 1971 | Find if Path Exists in Graph | Easy | Depth-First Search, Breadth-First Search, Union Find +1 |
Medium (123)
| # | Problem | Difficulty | Topics |
|---|---|---|---|
| 102 | Binary Tree Level Order Traversal | Medium | Tree, Breadth-First Search, Binary Tree |
| 103 | Binary Tree Zigzag Level Order Traversal | Medium | Tree, Breadth-First Search, Binary Tree |
| 107 | Binary Tree Level Order Traversal II | Medium | Tree, Breadth-First Search, Binary Tree |
| 116 | Populating Next Right Pointers in Each Node | Medium | Tree, Depth-First Search, Breadth-First Search +2 |
| 117 | Populating Next Right Pointers in Each Node II | Medium | Tree, Depth-First Search, Breadth-First Search +2 |
| 130 | Surrounded Regions | Medium | Depth-First Search, Breadth-First Search, Union Find +2 |
| 133 | Clone Graph | Medium | Depth-First Search, Breadth-First Search, Graph +1 |
| 199 | Binary Tree Right Side View | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
| 200 | Number of Islands | Medium | Depth-First Search, Breadth-First Search, Union Find +2 |
| 207 | Course Schedule | Medium | Depth-First Search, Breadth-First Search, Graph +1 |
| 210 | Course Schedule II | Medium | Depth-First Search, Breadth-First Search, Graph +1 |
| 279 | Perfect Squares | Medium | Breadth-First Search, Math, Dynamic Programming |
| 310 | Minimum Height Trees | Medium | Depth-First Search, Breadth-First Search, Graph +1 |
| 322 | Coin Change | Medium | Breadth-First Search, Array, Dynamic Programming |
| 365 | Water and Jug Problem | Medium | Depth-First Search, Breadth-First Search, Math |
| 399 | Evaluate Division | Medium | Depth-First Search, Breadth-First Search, Union Find +4 |
| 417 | Pacific Atlantic Water Flow | Medium | Depth-First Search, Breadth-First Search, Array +1 |
| 429 | N-ary Tree Level Order Traversal | Medium | Tree, Breadth-First Search |
| 433 | Minimum Genetic Mutation | Medium | Breadth-First Search, Hash Table, String |
| 449 | Serialize and Deserialize BST | Medium | Tree, Depth-First Search, Breadth-First Search +4 |
| 513 | Find Bottom Left Tree Value | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
| 515 | Find Largest Value in Each Tree Row | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
| 529 | Minesweeper | Medium | Depth-First Search, Breadth-First Search, Array +1 |
| 542 | 01 Matrix | Medium | Breadth-First Search, Array, Dynamic Programming +1 |
| 547 | Number of Provinces | Medium | Depth-First Search, Breadth-First Search, Union Find +1 |
| 623 | Add One Row to Tree | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
| 655 | Print Binary Tree | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
| 662 | Maximum Width of Binary Tree | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
| 672 | Bulb Switcher II | Medium | Bit Manipulation, Depth-First Search, Breadth-First Search +1 |
| 684 | Redundant Connection | Medium | Depth-First Search, Breadth-First Search, Union Find +1 |
| 690 | Employee Importance | Medium | Tree, Depth-First Search, Breadth-First Search +2 |
| 695 | Max Area of Island | Medium | Depth-First Search, Breadth-First Search, Union Find +2 |
| 721 | Accounts Merge | Medium | Depth-First Search, Breadth-First Search, Union Find +4 |
| 743 | Network Delay Time | Medium | Depth-First Search, Breadth-First Search, Graph +2 |
| 752 | Open the Lock | Medium | Breadth-First Search, Array, Hash Table +1 |
| 785 | Is Graph Bipartite? | Medium | Depth-First Search, Breadth-First Search, Union Find +1 |
| 787 | Cheapest Flights Within K Stops | Medium | Depth-First Search, Breadth-First Search, Graph +3 |
| 797 | All Paths From Source to Target | Medium | Depth-First Search, Breadth-First Search, Graph +1 |
| 802 | Find Eventual Safe States | Medium | Depth-First Search, Breadth-First Search, Graph +1 |
| 841 | Keys and Rooms | Medium | Depth-First Search, Breadth-First Search, Graph |
| 863 | All Nodes Distance K in Binary Tree | Medium | Tree, Depth-First Search, Breadth-First Search +2 |
| 865 | Smallest Subtree with all the Deepest Nodes | Medium | Tree, Depth-First Search, Breadth-First Search +2 |
| 886 | Possible Bipartition | Medium | Depth-First Search, Breadth-First Search, Union Find +1 |
| 909 | Snakes and Ladders | Medium | Breadth-First Search, Array, Matrix |
| 919 | Complete Binary Tree Inserter | Medium | Tree, Breadth-First Search, Design +1 |
| 934 | Shortest Bridge | Medium | Depth-First Search, Breadth-First Search, Array +1 |
| 958 | Check Completeness of a Binary Tree | Medium | Tree, Breadth-First Search, Binary Tree |
| 959 | Regions Cut By Slashes | Medium | Depth-First Search, Breadth-First Search, Union Find +3 |
| 967 | Numbers With Same Consecutive Differences | Medium | Breadth-First Search, Backtracking |
| 994 | Rotting Oranges | Medium | Breadth-First Search, Array, Matrix |
| 1020 | Number of Enclaves | Medium | Depth-First Search, Breadth-First Search, Union Find +2 |
| 1034 | Coloring A Border | Medium | Depth-First Search, Breadth-First Search, Array +1 |
| 1042 | Flower Planting With No Adjacent | Medium | Depth-First Search, Breadth-First Search, Graph |
| 1091 | Shortest Path in Binary Matrix | Medium | Breadth-First Search, Array, Matrix |
| 1123 | Lowest Common Ancestor of Deepest Leaves | Medium | Tree, Depth-First Search, Breadth-First Search +2 |
| 1129 | Shortest Path with Alternating Colors | Medium | Breadth-First Search, Graph |
| 1161 | Maximum Level Sum of a Binary Tree | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
| 1162 | As Far from Land as Possible | Medium | Breadth-First Search, Array, Dynamic Programming +1 |
| 1202 | Smallest String With Swaps | Medium | Depth-First Search, Breadth-First Search, Union Find +4 |
| 1254 | Number of Closed Islands | Medium | Depth-First Search, Breadth-First Search, Union Find +2 |
| 1261 | Find Elements in a Contaminated Binary Tree | Medium | Tree, Depth-First Search, Breadth-First Search +3 |
| 1267 | Count Servers that Communicate | Medium | Depth-First Search, Breadth-First Search, Union Find +3 |
| 1302 | Deepest Leaves Sum | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
| 1306 | Jump Game III | Medium | Depth-First Search, Breadth-First Search, Array |
| 1311 | Get Watched Videos by Your Friends | Medium | Breadth-First Search, Graph, Array +2 |
| 1315 | Sum of Nodes with Even-Valued Grandparent | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
| 1319 | Number of Operations to Make Network Connected | Medium | Depth-First Search, Breadth-First Search, Union Find +1 |
| 1361 | Validate Binary Tree Nodes | Medium | Tree, Depth-First Search, Breadth-First Search +3 |
| 1376 | Time Needed to Inform All Employees | Medium | Tree, Depth-First Search, Breadth-First Search |
| 1391 | Check if There is a Valid Path in a Grid | Medium | Depth-First Search, Breadth-First Search, Union Find +2 |
| 1443 | Minimum Time to Collect All Apples in a Tree | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
| 1448 | Count Good Nodes in Binary Tree | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
| 1457 | Pseudo-Palindromic Paths in a Binary Tree | Medium | Bit Manipulation, Tree, Depth-First Search +2 |
| 1462 | Course Schedule IV | Medium | Depth-First Search, Breadth-First Search, Graph +1 |
| 1466 | Reorder Routes to Make All Paths Lead to the City Zero | Medium | Depth-First Search, Breadth-First Search, Graph |
| 1519 | Number of Nodes in the Sub-Tree With the Same Label | Medium | Tree, Depth-First Search, Breadth-First Search +2 |
| 1559 | Detect Cycles in 2D Grid | Medium | Depth-First Search, Breadth-First Search, Union Find +2 |
| 1609 | Even Odd Tree | Medium | Tree, Breadth-First Search, Binary Tree |
| 1625 | Lexicographically Smallest String After Applying Operations | Medium | Depth-First Search, Breadth-First Search, String +1 |
| 1631 | Path With Minimum Effort | Medium | Depth-First Search, Breadth-First Search, Union Find +4 |
| 1654 | Minimum Jumps to Reach Home | Medium | Breadth-First Search, Array, Dynamic Programming |
| 1765 | Map of Highest Peak | Medium | Breadth-First Search, Array, Matrix |
| 1905 | Count Sub Islands | Medium | Depth-First Search, Breadth-First Search, Union Find +2 |
| 1926 | Nearest Exit from Entrance in Maze | Medium | Breadth-First Search, Array, Matrix |
| 1992 | Find All Groups of Farmland | Medium | Depth-First Search, Breadth-First Search, Array +1 |
| 1993 | Operations on Tree | Medium | Tree, Depth-First Search, Breadth-First Search +3 |
| 2039 | The Time When the Network Becomes Idle | Medium | Breadth-First Search, Graph, Array |
| 2059 | Minimum Operations to Convert Number | Medium | Breadth-First Search, Array |
| 2101 | Detonate the Maximum Bombs | Medium | Depth-First Search, Breadth-First Search, Graph +3 |
| 2146 | K Highest Ranked Items Within a Price Range | Medium | Breadth-First Search, Array, Matrix +2 |
| 2192 | All Ancestors of a Node in a Directed Acyclic Graph | Medium | Depth-First Search, Breadth-First Search, Graph +1 |
| 2316 | Count Unreachable Pairs of Nodes in an Undirected Graph | Medium | Depth-First Search, Breadth-First Search, Union Find +1 |
| 2368 | Reachable Nodes With Restrictions | Medium | Tree, Depth-First Search, Breadth-First Search +4 |
| 2385 | Amount of Time for Binary Tree to Be Infected | Medium | Tree, Depth-First Search, Breadth-First Search +2 |
| 2415 | Reverse Odd Levels of Binary Tree | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
| 2467 | Most Profitable Path in a Tree | Medium | Tree, Depth-First Search, Breadth-First Search +2 |
| 2471 | Minimum Number of Operations to Sort a Binary Tree by Level | Medium | Tree, Breadth-First Search, Binary Tree |
| 2477 | Minimum Fuel Cost to Report to the Capital | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
| 2492 | Minimum Score of a Path Between Two Cities | Medium | Depth-First Search, Breadth-First Search, Union Find +1 |
| 2556 | Disconnect Path in a Binary Matrix by at Most One Flip | Medium | Depth-First Search, Breadth-First Search, Array +2 |
| 2583 | Kth Largest Sum in a Binary Tree | Medium | Tree, Breadth-First Search, Binary Tree +1 |
| 2596 | Check Knight Tour Configuration | Medium | Depth-First Search, Breadth-First Search, Array +2 |
| 2641 | Cousins in Binary Tree II | Medium | Tree, Depth-First Search, Breadth-First Search +2 |
| 2658 | Maximum Number of Fish in a Grid | Medium | Depth-First Search, Breadth-First Search, Union Find +2 |
| 2685 | Count the Number of Complete Components | Medium | Depth-First Search, Breadth-First Search, Union Find +1 |
| 2812 | Find the Safest Path in a Grid | Medium | Breadth-First Search, Union Find, Array +3 |
| 2850 | Minimum Moves to Spread Stones Over Grid | Medium | Breadth-First Search, Array, Dynamic Programming +1 |
| 2998 | Minimum Number of Operations to Make X and Y Equal | Medium | Breadth-First Search, Memoization, Dynamic Programming |
| 261 | Graph Valid TreePremium | Medium | Depth-First Search, Breadth-First Search, Union Find +1 |
| 286 | Walls and GatesPremium | Medium | Breadth-First Search, Array, Matrix |
| 314 | Binary Tree Vertical Order TraversalPremium | Medium | Tree, Depth-First Search, Breadth-First Search +3 |
| 323 | Number of Connected Components in an Undirected GraphPremium | Medium | Depth-First Search, Breadth-First Search, Union Find +1 |
| 339 | Nested List Weight SumPremium | Medium | Depth-First Search, Breadth-First Search |
| 364 | Nested List Weight Sum IIPremium | Medium | Stack, Depth-First Search, Breadth-First Search |
| 490 | The MazePremium | Medium | Depth-First Search, Breadth-First Search, Array +1 |
| 505 | The Maze IIPremium | Medium | Depth-First Search, Breadth-First Search, Graph +4 |
| 582 | Kill ProcessPremium | Medium | Tree, Depth-First Search, Breadth-First Search +2 |
| 694 | Number of Distinct IslandsPremium | Medium | Depth-First Search, Breadth-First Search, Union Find +2 |
| 737 | Sentence Similarity IIPremium | Medium | Depth-First Search, Breadth-First Search, Union Find +3 |
| 742 | Closest Leaf in a Binary TreePremium | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
| 1087 | Brace ExpansionPremium | Medium | Stack, Breadth-First Search, String +2 |
| 1102 | Path With Maximum Minimum ValuePremium | Medium | Depth-First Search, Breadth-First Search, Union Find +4 |
| 1197 | Minimum Knight MovesPremium | Medium | Breadth-First Search |
Hard (58)
| # | Problem | Difficulty | Topics |
|---|---|---|---|
| 126 | Word Ladder II | Hard | Breadth-First Search, Hash Table, String +1 |
| 127 | Word Ladder | Hard | Breadth-First Search, Hash Table, String |
| 297 | Serialize and Deserialize Binary Tree | Hard | Tree, Depth-First Search, Breadth-First Search +3 |
| 301 | Remove Invalid Parentheses | Hard | Breadth-First Search, String, Backtracking |
| 329 | Longest Increasing Path in a Matrix | Hard | Depth-First Search, Breadth-First Search, Graph +5 |
| 407 | Trapping Rain Water II | Hard | Breadth-First Search, Array, Matrix +1 |
| 488 | Zuma Game | Hard | Stack, Breadth-First Search, Memoization +2 |
| 514 | Freedom Trail | Hard | Depth-First Search, Breadth-First Search, String +1 |
| 675 | Cut Off Trees for Golf Event | Hard | Breadth-First Search, Array, Matrix +1 |
| 685 | Redundant Connection II | Hard | Depth-First Search, Breadth-First Search, Union Find +1 |
| 749 | Contain Virus | Hard | Depth-First Search, Breadth-First Search, Array +2 |
| 765 | Couples Holding Hands | Hard | Greedy, Depth-First Search, Breadth-First Search +2 |
| 773 | Sliding Puzzle | Hard | Breadth-First Search, Memoization, Array +3 |
| 778 | Swim in Rising Water | Hard | Depth-First Search, Breadth-First Search, Union Find +4 |
| 815 | Bus Routes | Hard | Breadth-First Search, Array, Hash Table |
| 827 | Making A Large Island | Hard | Depth-First Search, Breadth-First Search, Union Find +2 |
| 839 | Similar String Groups | Hard | Depth-First Search, Breadth-First Search, Union Find +3 |
| 847 | Shortest Path Visiting All Nodes | Hard | Bit Manipulation, Breadth-First Search, Graph +2 |
| 854 | K-Similar Strings | Hard | Breadth-First Search, Hash Table, String |
| 864 | Shortest Path to Get All Keys | Hard | Bit Manipulation, Breadth-First Search, Array +1 |
| 924 | Minimize Malware Spread | Hard | Depth-First Search, Breadth-First Search, Union Find +3 |
| 928 | Minimize Malware Spread II | Hard | Depth-First Search, Breadth-First Search, Union Find +3 |
| 987 | Vertical Order Traversal of a Binary Tree | Hard | Tree, Depth-First Search, Breadth-First Search +3 |
| 1036 | Escape a Large Maze | Hard | Depth-First Search, Breadth-First Search, Array +1 |
| 1096 | Brace Expansion II | Hard | Stack, Breadth-First Search, Hash Table +3 |
| 1203 | Sort Items by Groups Respecting Dependencies | Hard | Depth-First Search, Breadth-First Search, Graph +1 |
| 1210 | Minimum Moves to Reach Target with Rotations | Hard | Breadth-First Search, Array, Matrix |
| 1263 | Minimum Moves to Move a Box to Their Target Location | Hard | Breadth-First Search, Array, Matrix +1 |
| 1284 | Minimum Number of Flips to Convert Binary Matrix to Zero Matrix | Hard | Bit Manipulation, Breadth-First Search, Array +2 |
| 1293 | Shortest Path in a Grid with Obstacles Elimination | Hard | Breadth-First Search, Array, Matrix |
| 1298 | Maximum Candies You Can Get from Boxes | Hard | Breadth-First Search, Graph, Array |
| 1345 | Jump Game IV | Hard | Breadth-First Search, Array, Hash Table |
| 1368 | Minimum Cost to Make at Least One Valid Path in a Grid | Hard | Breadth-First Search, Graph, Array +3 |
| 1377 | Frog Position After T Seconds | Hard | Tree, Depth-First Search, Breadth-First Search +1 |
| 1483 | Kth Ancestor of a Tree Node | Hard | Bit Manipulation, Tree, Depth-First Search +4 |
| 1568 | Minimum Number of Days to Disconnect Island | Hard | Depth-First Search, Breadth-First Search, Array +2 |
| 1970 | Last Day Where You Can Still Cross | Hard | Depth-First Search, Breadth-First Search, Union Find +3 |
| 2045 | Second Minimum Time to Reach Destination | Hard | Breadth-First Search, Graph, Shortest Path |
| 2092 | Find All People With Secret | Hard | Depth-First Search, Breadth-First Search, Union Find +2 |
| 2258 | Escape the Spreading Fire | Hard | Breadth-First Search, Array, Binary Search +1 |
| 2290 | Minimum Obstacle Removal to Reach Corner | Hard | Breadth-First Search, Graph, Array +3 |
| 2328 | Number of Increasing Paths in a Grid | Hard | Depth-First Search, Breadth-First Search, Graph +5 |
| 2360 | Longest Cycle in a Graph | Hard | Depth-First Search, Breadth-First Search, Graph +1 |
| 2458 | Height of Binary Tree After Subtree Removal Queries | Hard | Tree, Depth-First Search, Breadth-First Search +2 |
| 2493 | Divide Nodes Into the Maximum Number of Groups | Hard | Depth-First Search, Breadth-First Search, Union Find +1 |
| 2503 | Maximum Number of Points From Grid Queries | Hard | Breadth-First Search, Union Find, Array +4 |
| 2577 | Minimum Time to Visit a Cell In a Grid | Hard | Breadth-First Search, Graph, Array +3 |
| 2608 | Shortest Cycle in a Graph | Hard | Breadth-First Search, Graph |
| 2612 | Minimum Reverse Operations | Hard | Breadth-First Search, Union Find, Array +2 |
| 2617 | Minimum Number of Visited Cells in a Grid | Hard | Stack, Breadth-First Search, Union Find +5 |
| 2858 | Minimum Edge Reversals So Every Node Is Reachable | Hard | Depth-First Search, Breadth-First Search, Graph +1 |
| 269 | Alien DictionaryPremium | Hard | Depth-First Search, Breadth-First Search, Graph +3 |
| 302 | Smallest Rectangle Enclosing Black PixelsPremium | Hard | Depth-First Search, Breadth-First Search, Array +2 |
| 317 | Shortest Distance from All BuildingsPremium | Hard | Breadth-First Search, Array, Matrix |
| 428 | Serialize and Deserialize N-ary TreePremium | Hard | Tree, Depth-First Search, Breadth-First Search +1 |
| 431 | Encode N-ary Tree to Binary TreePremium | Hard | Tree, Depth-First Search, Breadth-First Search +2 |
| 499 | The Maze IIIPremium | Hard | Depth-First Search, Breadth-First Search, Graph +5 |
| 711 | Number of Distinct Islands IIPremium | Hard | Depth-First Search, Breadth-First Search, Union Find +2 |
Keep exploring
All LeetCode topicsEvery tag with a page of its own, with the number of problems behind each.LeetCode patternsThe techniques themselves, with a Python template and complexity for each.Curated study listsBlind 75, NeetCode 150 and three more, grouped by pattern.Easy problemsStart here when the data structure is new rather than the problem.
Other topics
- Array1,569
- String672
- Hash Table588
- Math485
- Dynamic Programming481
- Sorting392
- Greedy346
- Depth-First Search289
- Binary Search253
- Database249
- Tree225
- Matrix216
- Two Pointers201
- Bit Manipulation194
- Binary Tree174
- Heap (Priority Queue)163
- Prefix Sum157
- Stack157
- Simulation144
- Graph138
- Counting126
- Design122
- Sliding Window116
- Backtracking105
When the Breadth-First Search problem arrives live
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