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L5 Prep

Week 03 — Core patterns II: trees & graphs

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Goal: graphs are Google’s favorite category. Own them.

  • Topics: binary trees (traversals, LCA, path sums, serialization), BST invariants, tries, BFS/DFS on grids and graphs, topological sort, union-find, Dijkstra, cycle detection.
  • 14–16 problems. At least 6 must be grid/matrix problems — Google loves them.
  • Implement from memory, no reference: union-find with path compression + union by rank, Dijkstra with a heap, Kahn’s topological sort.
  • System design: building blocks — load balancing, caching, CDN, SQL vs NoSQL, replication, sharding. One page of notes per topic in your own words (06-system-design-reference.md has the depth; write yours from it, don’t copy it).
  • Behavioral: 3 more STAR stories (target: 6 total).

Exit criteria: you can write union-find and Dijkstra cold, correctly, in under 10 minutes each.