Graphs & Trees

BFS, DFS, shortest paths, components and tree queries.

46 problems

Title	Tags	Acceptance	Difficulty
1. Count Binary Search Trees	Catalan	—	Medium
2. Shortest Path (Unweighted)	BFS	—	Easy
3. Connected Components	DFS · Union-Find	—	Easy
4. Cycle in an Undirected Graph	Union-Find · DFS	—	Medium
5. Cycle in a Directed Graph	Topological Sort	—	Medium
6. Topological Order	Topological Sort	—	Medium
7. Shortest Path (Weighted)	Dijkstra	—	Medium
8. Minimum Spanning Tree	Kruskal · Union-Find	—	Medium
9. Is the Graph Bipartite?	BFS · Colouring	—	Medium
10. Diameter of a Tree	BFS · Trees	—	Medium
11. Tree Height from Parent Array	Trees	—	Easy
12. Friend Circles	DFS · Adjacency Matrix	—	Easy
13. Rotting Oranges	Multi-source BFS	—	Medium
14. Count Regions of Same Colour	DFS · Flood Fill	—	Easy
15. Word Ladder	BFS	—	Hard
16. Lowest Common Ancestor	Trees · LCA	—	Hard
17. Paths in a DAG	Topological Sort · DP	—	Medium
18. Knight's Shortest Path	BFS	—	Medium
19. Snakes and Ladders	BFS	—	Hard
20. Inorder Traversal	Binary Tree · DFS	—	Easy
21. Preorder Traversal	Binary Tree · DFS	—	Easy
22. Postorder Traversal	Binary Tree · DFS	—	Easy
23. Level Order by Lines	BFS	—	Easy
24. Zigzag Level Order	BFS	—	Medium
25. Maximum Depth of a Binary Tree	DFS	—	Easy
26. Minimum Depth	BFS	—	Easy
27. Count and Sum of Nodes	Traversal	—	Easy
28. Count Leaves	Traversal	—	Easy
29. Symmetric Tree	Recursion	—	Easy
30. Height-Balanced Tree	DFS	—	Easy
31. Diameter of a Binary Tree	DFS	—	Easy
32. Root-to-Leaf Path Sum	DFS	—	Easy
33. Validate a BST	BST · Inorder	—	Medium
34. K-th Smallest in a BST	BST · Inorder	—	Medium
35. LCA in a BST	BST	—	Easy
36. Build a BST by Insertion	BST	—	Easy
37. Range Sum of a BST	BST · DFS	—	Easy
38. Right Side View	BFS	—	Medium
39. Left Side View	BFS	—	Easy
40. Level Sums and Widest Level	BFS	—	Medium
41. Same Tree	Recursion	—	Easy
42. K Largest Elements	Heap	—	Easy
43. Merge K Sorted Lists	Heap · Merge	—	Hard
44. Connect Ropes at Minimum Cost	Heap · Greedy	—	Medium
45. K-th Largest in a Stream	Heap	—	Medium
46. Task Scheduler	Greedy · Counting	—	Medium

46 of 46 problems