Lesson 100
DFS vs BFS
Stack vs Queue · Deep vs Wide
1:00How depth-first search and breadth-first search differ by one data structure, and when to reach for each.
By the end, you can
- Explain the single code difference between DFS and BFS and why it changes the visit order.
- Trace the DFS and BFS visit order on a small graph by hand.
- State that both algorithms have O(V + E) time complexity.
- Compare the space complexity of DFS (O(h) on a tree) and BFS (O(width)) and explain when DFS uses less memory.
- Explain why BFS guarantees the shortest path in an unweighted graph, and why DFS does not.
- Identify which scenarios call for BFS and which call for DFS using the decision framework.
- Describe why Dijkstra is needed when edges carry different weights.
- Explain the cycle trap and state the correct time to mark a node as visited.
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