AlgoSolveoRoadmap › Stage 8: Graphs › Pattern 37 of 53
DSA pattern guide
Graph — DFS
Count islands or components, flood fill, reachability, bipartite.
Use it when
Count islands or components, flood fill, reachability, bipartite.
Key idea
Visit a node, mark it, recurse to unvisited neighbours. Each fresh start is a new component.
Practice problems, in order
- Flood FillEasy
- Number of IslandsMedium
- All Paths from Source to TargetMedium
- Find Eventual Safe StatesMedium
- Count ProvincesMedium
- Surrounded RegionsMedium
- Is Graph BipartiteMedium
- Max Area of IslandMedium
- Pacific Atlantic Water FlowMedium
- Critical Connections in a NetworkHard
How to practise this pattern
- Read the problem and look for the signal above before writing any code.
- Say the brute force out loud, with its time complexity, then ask what work it repeats.
- Apply the key idea and write the optimised version yourself.
- If you're stuck for more than 10 minutes, take one small hint, not the full solution.
- Move to the next problem only when you can explain why this pattern fits.
Stuck on one of these?
The AlgoSolveo extension (free, launching soon) sits beside the LeetCode problem and gives the smallest hint that gets you moving, never the full answer. Solved problems tick off on your roadmap.
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