Day 13 part 1.

src/day13.rs

@@ -0,0 +1,82 @@
+use std::collections::{HashMap, HashSet};
+
+use aoc_runner_derive::{aoc, aoc_generator};
+
+#[aoc_generator(day13)]
+fn parse(input: &str) -> HashMap<(String, String), i32> {
+    input.lines()
+        .map(|line| {
+            let v: Vec<&str> = line[0..line.len() - 1].split(" ").collect();
+            let from = v[0];
+            let to = v[10];
+            let mut value = v[3].parse::<i32>().unwrap();
+            if v[2] == "lose" {
+                value *= -1;
+            }
+            ((from.into(), to.into()), value)
+        }).collect()
+}
+
+#[aoc(day13, part1)]
+fn part1(deltas: &HashMap<(String, String), i32>) -> i32 {
+    let names: HashSet<_> = deltas.keys().map(|s| s.0.clone()).collect();
+    permutations(names).iter().map(|arrangement| {
+        let mut happiness = 0;
+        for i in 0..arrangement.len() {
+            let left = if i == 0 { arrangement.len() - 1 } else { i - 1 };
+            let right = (i + 1) % arrangement.len();
+            happiness += deltas[&(arrangement[left].clone(), arrangement[i].clone())] +
+                deltas[&(arrangement[i].clone(), arrangement[left].clone())];
+        }
+        happiness
+    }).max().unwrap()
+}
+
+fn permutations(values: HashSet<String>) -> Vec<Vec<String>> {
+    let base: Vec<String> = values.into_iter().collect();
+    p(base)
+}
+
+fn p(mut input: Vec<String>) -> Vec<Vec<String>> {
+    if input.len() == 1 {
+        return vec![input];
+    }
+    let mut results = Vec::new();
+    for _ in 0..input.len() {
+        p(input.iter().skip(1).map(|t| t.clone()).collect()).into_iter().for_each(|mut v| {
+            v.insert(0, input[0].clone());
+            results.push(v);
+        });
+        let v = input.remove(0);
+        input.push(v);
+    }
+    results
+}
+
+
+// #[aoc(day13, part2)]
+// fn part2(input: &str) -> String {
+//     todo!()
+// }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_part1() {
+        let input = "Alice would gain 54 happiness units by sitting next to Bob.
+Alice would lose 79 happiness units by sitting next to Carol.
+Alice would lose 2 happiness units by sitting next to David.
+Bob would gain 83 happiness units by sitting next to Alice.
+Bob would lose 7 happiness units by sitting next to Carol.
+Bob would lose 63 happiness units by sitting next to David.
+Carol would lose 62 happiness units by sitting next to Alice.
+Carol would gain 60 happiness units by sitting next to Bob.
+Carol would gain 55 happiness units by sitting next to David.
+David would gain 46 happiness units by sitting next to Alice.
+David would lose 7 happiness units by sitting next to Bob.
+David would gain 41 happiness units by sitting next to Carol.";
+        assert_eq!(part1(&parse(input)), 330);
+    }
+}

src/lib.rs

@@ -5,5 +5,6 @@ extern crate aoc_runner_derive;
 mod day10;
 mod day11;
 mod day12;
+mod day13;
 
 aoc_lib! { year = 2015 }