Dfs

Hook

Explore a corridor fully before returning to its junction.

Watch

Finish a branch before returning. Edit the graph JSON to add a cycle, isolate a vertex or change an edge weight. Nodes are numbered from zero.

How it works

1. Enter and mark one vertex.
2. Recurse into each still-unseen neighbor.
3. Return after all of its outgoing neighbors have been considered.

Try it

Predict the next frontier decision or edge operation before revealing it. Compare a connected graph with the same graph after removing an important edge.

Complexity

O(V+E) time and O(V) traversal workspace. Each vertex is entered once and each outgoing edge is considered once. Recursive activations retain the current branch until it is fully explored. The counters count teaching operations; animation duration is not a CPU benchmark.

Code

The four references show the core operation. Adjacency-list inputs use zero-based vertex indices. Weighted references use (neighbor,weight) pairs or explicit edge triples. Validate the graph assumptions before calling standalone code.

When to use

Use for reachability, finish orders and structural graph analysis.

Interview pitfalls

DFS discovery depth is not generally a shortest-path distance.

Quiz

Check the graph assumptions, invariant and boundary conditions below.