Day 24: I will build the strongest lego-bridge in the galaxy!

2 files changed, 111 insertions, 0 deletions

diff --git a/inputs/day_24.txt b/inputs/day_24.txt
new file mode 100644
index 0000000..1fbfe25
--- /dev/null
+++ b/inputs/day_24.txt
@@ -0,0 +1,57 @@
+42/37
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+1/10
diff --git a/src/bin/day_24.rs b/src/bin/day_24.rs
index 1fc3eca..eb7fddd 100644
--- a/src/bin/day_24.rs
+++ b/src/bin/day_24.rs
@@ -3,4 +3,58 @@ use advent_of_code_2017::*;
 
 fn main() {
     let args = AdventArgs::init();
+    let components: Vec<Component> = args.input.iter()
+        .map(|line| {
+            let mut split = line.split('/');
+            Component {
+                a: split.next().unwrap().parse().unwrap(),
+                b: split.next().unwrap().parse().unwrap()
+            }
+        })
+        .collect();
+
+    if args.part == 1 {
+        let strongest = build_strongest(0, components);
+        println!("{}", strongest);
+    } else {
+        let (strongest, longest) = build_longest(0, components);
+        println!("length: {}, strength: {}", longest, strongest);
+    }
+}
+
+fn build_strongest(start: u32, components: Vec<Component>) -> u32 {
+    components.iter().enumerate()
+        .filter(|&(_, c)| c.a == start || c.b == start)
+        .map(|(i, c)| {
+            let end = if c.a == start { c.b } else { c.a };
+            let mut subset = components.clone();
+            subset.remove(i);
+            c.strength() + build_strongest(end, subset)
+        }).max().unwrap_or(0)
+}
+
+fn build_longest(start: u32, components: Vec<Component>) -> (u32, u32) {
+    components.iter().enumerate()
+        .filter(|&(_, c)| c.a == start || c.b == start)
+        .map(|(i, c)| {
+            let end = if c.a == start { c.b } else { c.a };
+            let mut subset = components.clone();
+            subset.remove(i);
+            let (s, l) = build_longest(end, subset);
+            (c.strength() + s, 1 + l)
+        }).max_by(|&(s1, l1), &(s2, l2)| {
+            l1.cmp(&l2).then(s1.cmp(&s2))
+        }).unwrap_or((0, 0))
+}
+
+#[derive(Debug, Clone)]
+struct Component {
+    a: u32,
+    b: u32
+}
+
+impl Component {
+    fn strength(&self) -> u32 {
+        self.a + self.b
+    }
 }