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dfs-vs-bfs

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Choose between DFS and BFS for graph traversal problems. Use when deciding whether to explore depth-first (cycle detection, paths) or breadth-first (shortest path, levels).

General

What this skill does


## When to use

DFS (stack/recursion) explores one branch fully before backtracking. BFS (queue) explores level-by-level.

## Rules

- If the problem asks "shortest" or "minimum steps" on an unweighted graph, ALWAYS choose BFS
- If it asks "all paths," "can we reach," or "count islands," DFS is simpler
- NEVER use BFS for cycle detection — DFS is the right tool
- Both visit each node once: O(V+E) time

## DFS use cases

Cycle detection, topological sort, path existence, connected components, backtracking puzzles, flood fill.

## BFS use cases

Shortest unweighted path, level-order traversal, nearest neighbor, minimum steps.

## Example

"Count islands" → DFS flood-fill on 2D grid. "Shortest path in maze" → BFS with queue tracking (row, col, distance).
Files: 1
Size: 1.3 KB
Complexity: 10/100
Category: General

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