1 files changed, 49 insertions, 0 deletions
diff --git a/challenge-285/ppentchev/rust/src/ch-1.rs b/challenge-285/ppentchev/rust/src/ch-1.rs
new file mode 100644
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+++ b/challenge-285/ppentchev/rust/src/ch-1.rs
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+// SPDX-FileCopyrightText: Peter Pentchev <roam@ringlet.net>
+// SPDX-License-Identifier: BSD-2-Clause
+//! Solve the first task for week 285, "No Connection".
+
+use std::collections::HashSet;
+
+use tracing::{debug, trace};
+
+use crate::defs::Error;
+
+/// Week 285 task 1: No Connection.
+///
+/// # Errors
+///
+/// [`Error::NotImplemented`] so far.
+#[tracing::instrument(skip(routes))]
+#[inline]
+pub fn solve_no_connection(routes: &[(String, String)]) -> Result<String, Error> {
+    debug!(
+        "About to look for a leaf destination in {count} routes",
+        count = routes.len()
+    );
+    let (set_from, set_to) = routes.iter().fold(
+        (HashSet::new(), HashSet::new()),
+        |(mut set_from, mut set_to): (HashSet<&str>, HashSet<&str>),
+         &(ref route_from, ref route_to)| {
+            set_from.insert(route_from.as_ref());
+            set_to.insert(route_to.as_ref());
+            (set_from, set_to)
+        },
+    );
+    trace!("from: {count}", count = set_from.len());
+    trace!("to: {count}", count = set_to.len());
+
+    let mut diff = set_to.difference(&set_from);
+    let first = diff
+        .next()
+        .ok_or_else(|| Error::NoSolution("Not even a single leaf destination".to_owned()))?;
+    trace!(first);
+    diff.next().map_or_else(
+        || Ok((*first).to_owned()),
+        |second| {
+            trace!(second);
+            Err(Error::NoSolution(
+                "More than one leaf destination".to_owned(),
+            ))
+        },
+    )
+}