2017: Day 24

Author: michel-kraemer

2017/day24/.vscode/settings.json

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+{
+  "[rust]": {
+    "editor.defaultFormatter": "rust-lang.rust-analyzer",
+    "editor.formatOnSave": true
+  },
+  "rust-analyzer.check.command": "clippy"
+}

2017/day24/Cargo.lock

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+[package]
+name = "day24"
+version = "0.1.0"
+edition = "2021"

2017/day24/Cargo.toml

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+use std::{
+    collections::{HashSet, VecDeque},
+    fs,
+};
+
+struct State {
+    e: usize,
+    strength: usize,
+    seen: HashSet<(usize, usize)>,
+}
+
+fn main() {
+    let input = fs::read_to_string("input.txt").expect("Could not read file");
+    let bridges = input
+        .lines()
+        .map(|l| {
+            let p = l.split_once('/').unwrap();
+            (p.0.parse::<usize>().unwrap(), p.1.parse::<usize>().unwrap())
+        })
+        .collect::<Vec<_>>();
+
+    let mut queue = VecDeque::new();
+    queue.push_back(State {
+        e: 0,
+        strength: 0,
+        seen: HashSet::new(),
+    });
+
+    let mut max = 0;
+    let mut longest = 0;
+    let mut longest_max = 0;
+
+    while !queue.is_empty() {
+        let s = queue.pop_back().unwrap();
+
+        if s.strength > max {
+            max = s.strength;
+        }
+
+        if s.seen.len() > longest {
+            longest = s.seen.len();
+            longest_max = s.strength;
+        } else if s.seen.len() == longest && s.strength > longest_max {
+            longest_max = s.strength;
+        }
+
+        for b in &bridges {
+            if (b.0 == s.e || b.1 == s.e) && !s.seen.contains(b) {
+                let mut ns = s.seen.clone();
+                ns.insert(*b);
+                let s = State {
+                    e: if s.e == b.1 { b.0 } else { b.1 },
+                    strength: s.strength + b.0 + b.1,
+                    seen: ns,
+                };
+                queue.push_back(s);
+            }
+        }
+    }
+
+    // part 1
+    println!("{}", max);
+
+    // part 2
+    println!("{}", longest_max);
+}