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42 worked problems

Graphs

BFS, DFS, shortest paths and spanning trees. Entities form arbitrary connections and the task asks about reachability, ordering, shortest paths, or connectivity.

Recognition signal

When should you think of Graphs?

Entities form arbitrary connections and the task asks about reachability, ordering, shortest paths, or connectivity.

Core invariant

What must stay true?

Visited or distance state records the strongest fact proven for each vertex so far.

Practice in a deliberate order

Starter

Build the template

  1. #733 Flood FillEasy
  2. #1971 Find if Path Exists in GraphEasy
  3. GFG DFS of GraphEasy
  4. GFG BFS of GraphEasy
Core

Recognize variations

  1. #130 Surrounded RegionsMedium
  2. #133 Clone GraphMedium
  3. #200 Number of IslandsMedium
  4. #207 Course ScheduleMedium
  5. #210 Course Schedule IIMedium
  6. #417 Pacific Atlantic Water FlowMedium
Stretch

Combine ideas under pressure

  1. #127 Word LadderHard
  2. #332 Reconstruct ItineraryHard
  3. #778 Swim in Rising WaterHard
  4. GFG Strongly Connected Components (Kosaraju)Hard

What to learn in this cluster

  1. 01BFS and DFS
  2. 02Topological order and components
  3. 03Shortest paths and spanning trees

All Graphs problems

42 of 42 walkthroughs
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