📦 Data Structures
Stacks, queues, hash maps and trees — implement and run them.
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Lesson 1 — Stack
easy · 8 min
Lesson 2 — Queue
easy · 8 min
Lesson 3 — Hash map
medium · 9 min
Lesson 4 — Sets
medium · 8 min
Lesson 5 — Stacks
medium · 9 min
Lesson 6 — Set operations
medium · 9 min
Lesson 7 — Frequency map
medium · 9 min
Lesson 8 — Graph as adjacency list
medium · 9 min
Lesson 9 — Linked list
hard · 12 min
Lesson 10 — Binary tree
hard · 12 min
Lesson 11 — Queues
hard · 10 min
Lesson 12 — Hash maps
hard · 11 min
Lesson 13 — Linked list
hard · 12 min
Lesson 14 — Binary tree
hard · 13 min
Lesson 15 — Heap / priority
hard · 12 min
Lesson 16 — Matrix traversal
hard · 11 min
Lesson 17 — Mini project: unique words
hard · 12 min
Lesson 18 — BFS traversal
hard · 11 min
Lesson 19 — DFS traversal
hard · 11 min
Lesson 20 — Union-Find
hard · 12 min
Lesson 21 — Min-heap
hard · 11 min
Lesson 22 — Trie (expert)
hard · 13 min
Lesson 23 — Validate a BST
very hard · 15 min
Lesson 24 — LRU cache
very hard · 15 min
Lesson 25 — Ultimate: build a min-heap
★ ultimate · 20 min