Problem

CNAME / Redirect Chain Resolver (Rust)

Topics: graphs, chain walk, loop detection

Problem

A name server (or an HTTP redirect follower) chases a CNAME/Location chain: each name points at the next until one has no further record — the canonical target. Walk the chain from a start name to that target, but refuse to chase forever.

pub enum ResolveError { Loop(Vec<String>), TooLong(usize) }
pub fn resolve(cnames: &BTreeMap<String, String>, start: &str, max_hops: usize)
    -> Result<String, ResolveError>;

cnames maps a name to the single name it redirects to. A name with no entry is the canonical target; resolving it returns itself (zero hops).
Each hop follows one link. Return Err(TooLong(max_hops)) if resolving would follow more than max_hops links.
Return Err(Loop(chain)) if the chain revisits a name (including a name that points to itself); chain is the names visited, in order, before the repeat.

{www→example.com, example.com→lb-01}; start=www, max_hops=10  → "lb-01"
{a→b, b→a}; start=a                                            → Err(Loop(["a","b"]))
{a→b, b→c, c→d}; start=a, max_hops=2                           → Err(TooLong(2))

It's a single walk down a linked chain: keep a seen set to catch loops and a hop counter to cap the length.

Grading

Your solution.rs is compiled together with a trusted tests.rs (which include!s it) using rustc --test. Only solution.rs is yours to edit.

Leaderboard score: lower is better, 1.0 ≈ reference

#	Name	score	ns/op	allocs

Output

No submission yet.