BFS Vs DFS

 

📊 Comparison of BFS and DFS

FeatureBFS (Breadth First Search)DFS (Depth First Search)
DefinitionExplores neighbors first (level by level).Explores as far as possible along one branch before backtracking.
Data Structure UsedQueue (FIFO).Stack (explicit stack or recursion).
Traversal OrderVisits nodes in increasing "distance" from the source.Visits nodes by diving deep into a path before exploring siblings.
Typical Output ExampleSource → Neighbors → Next level …Source → First child → Child’s child … backtrack …
Time ComplexityO(V + E) (same as DFS).O(V + E) (same as BFS).
Space ComplexityO(V) (queue stores many nodes at a time, worst case).O(V) (stack/recursion depth).
Shortest PathYes ✅ (in unweighted graphs, BFS finds shortest path).No ❌ (DFS does not guarantee shortest path).
CompletenessAlways finds a solution if one exists.May not find shortest solution; may get trapped without visited checks.
Application Areas- Shortest path in unweighted graphs
- Level order traversal in trees
- Networking (broadcasting, routing)		- Topological sorting
- Detecting cycles
- Solving puzzles/mazes
- Path existence checking
Best ForProblems requiring shortest path or level-order info.Problems requiring exhaustive search or backtracking.

👉 Quick intuition for students:

  • BFS = “spreading out layer by layer” (like ripples in water).

  • DFS = “diving deep into a path” before coming back up.

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