From 6d39fd641189b78277eaaa5ba4c3cbe5f2f1f51a Mon Sep 17 00:00:00 2001
From: timeshifter <timeshifter@sumatrae>
Date: Tue, 23 Jun 2026 18:05:36 +0200
Subject: [PATCH] add day 13

---
 day13/Cargo.lock  | 25 ++++++++++++++
 day13/Cargo.toml  |  7 ++++
 day13/input.txt   | 56 ++++++++++++++++++++++++++++++++
 day13/src/main.rs | 83 +++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 171 insertions(+)
 create mode 100644 day13/Cargo.lock
 create mode 100644 day13/Cargo.toml
 create mode 100644 day13/input.txt
 create mode 100644 day13/src/main.rs

diff --git a/day13/Cargo.lock b/day13/Cargo.lock
new file mode 100644
index 0000000..3415aa7
--- /dev/null
+++ b/day13/Cargo.lock
@@ -0,0 +1,25 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "day13"
+version = "0.1.0"
+dependencies = [
+ "itertools",
+]
+
+[[package]]
+name = "either"
+version = "1.16.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "91622ff5e7162018101f2fea40d6ebf4a78bbe5a49736a2020649edf9693679e"
+
+[[package]]
+name = "itertools"
+version = "0.15.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8b4baf93f58d4425749ca49a51c50ebab072c5df6994d08fed93541c331481dc"
+dependencies = [
+ "either",
+]
diff --git a/day13/Cargo.toml b/day13/Cargo.toml
new file mode 100644
index 0000000..93889a6
--- /dev/null
+++ b/day13/Cargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "day13"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+itertools = "*"
diff --git a/day13/input.txt b/day13/input.txt
new file mode 100644
index 0000000..9ddfd38
--- /dev/null
+++ b/day13/input.txt
@@ -0,0 +1,56 @@
+Alice would lose 2 happiness units by sitting next to Bob.
+Alice would lose 62 happiness units by sitting next to Carol.
+Alice would gain 65 happiness units by sitting next to David.
+Alice would gain 21 happiness units by sitting next to Eric.
+Alice would lose 81 happiness units by sitting next to Frank.
+Alice would lose 4 happiness units by sitting next to George.
+Alice would lose 80 happiness units by sitting next to Mallory.
+Bob would gain 93 happiness units by sitting next to Alice.
+Bob would gain 19 happiness units by sitting next to Carol.
+Bob would gain 5 happiness units by sitting next to David.
+Bob would gain 49 happiness units by sitting next to Eric.
+Bob would gain 68 happiness units by sitting next to Frank.
+Bob would gain 23 happiness units by sitting next to George.
+Bob would gain 29 happiness units by sitting next to Mallory.
+Carol would lose 54 happiness units by sitting next to Alice.
+Carol would lose 70 happiness units by sitting next to Bob.
+Carol would lose 37 happiness units by sitting next to David.
+Carol would lose 46 happiness units by sitting next to Eric.
+Carol would gain 33 happiness units by sitting next to Frank.
+Carol would lose 35 happiness units by sitting next to George.
+Carol would gain 10 happiness units by sitting next to Mallory.
+David would gain 43 happiness units by sitting next to Alice.
+David would lose 96 happiness units by sitting next to Bob.
+David would lose 53 happiness units by sitting next to Carol.
+David would lose 30 happiness units by sitting next to Eric.
+David would lose 12 happiness units by sitting next to Frank.
+David would gain 75 happiness units by sitting next to George.
+David would lose 20 happiness units by sitting next to Mallory.
+Eric would gain 8 happiness units by sitting next to Alice.
+Eric would lose 89 happiness units by sitting next to Bob.
+Eric would lose 69 happiness units by sitting next to Carol.
+Eric would lose 34 happiness units by sitting next to David.
+Eric would gain 95 happiness units by sitting next to Frank.
+Eric would gain 34 happiness units by sitting next to George.
+Eric would lose 99 happiness units by sitting next to Mallory.
+Frank would lose 97 happiness units by sitting next to Alice.
+Frank would gain 6 happiness units by sitting next to Bob.
+Frank would lose 9 happiness units by sitting next to Carol.
+Frank would gain 56 happiness units by sitting next to David.
+Frank would lose 17 happiness units by sitting next to Eric.
+Frank would gain 18 happiness units by sitting next to George.
+Frank would lose 56 happiness units by sitting next to Mallory.
+George would gain 45 happiness units by sitting next to Alice.
+George would gain 76 happiness units by sitting next to Bob.
+George would gain 63 happiness units by sitting next to Carol.
+George would gain 54 happiness units by sitting next to David.
+George would gain 54 happiness units by sitting next to Eric.
+George would gain 30 happiness units by sitting next to Frank.
+George would gain 7 happiness units by sitting next to Mallory.
+Mallory would gain 31 happiness units by sitting next to Alice.
+Mallory would lose 32 happiness units by sitting next to Bob.
+Mallory would gain 95 happiness units by sitting next to Carol.
+Mallory would gain 91 happiness units by sitting next to David.
+Mallory would lose 66 happiness units by sitting next to Eric.
+Mallory would lose 75 happiness units by sitting next to Frank.
+Mallory would lose 99 happiness units by sitting next to George.
diff --git a/day13/src/main.rs b/day13/src/main.rs
new file mode 100644
index 0000000..67ffe99
--- /dev/null
+++ b/day13/src/main.rs
@@ -0,0 +1,83 @@
+use std::collections::HashSet;
+
+use itertools::Itertools;
+
+fn main() {
+    let mut data: Vec<_> = std::fs::read_to_string("input.txt")
+        .unwrap()
+        .lines()
+        .map(Neighbors::parse)
+        .collect();
+
+    part1(&data);
+
+    let persons: HashSet<_> = data.iter().map(|p| p.persons.0.clone()).collect();
+    for p in &persons {
+        data.push(Neighbors::new(("me".to_string(), p.to_string()), 0));
+        data.push(Neighbors::new((p.to_string(), "me".to_string()), 0));
+    }
+
+    part1(&data);
+}
+
+fn part1(data: &[Neighbors]) {
+    let persons: HashSet<_> = data.iter().map(|p| p.persons.0.clone()).collect();
+
+    let result = persons
+        .iter()
+        .permutations(persons.len())
+        .map(|order| calculate_happiness(&order, data))
+        .max()
+        .unwrap();
+
+    println!("{result}");
+}
+
+fn calculate_happiness(order: &[&String], neighbors: &[Neighbors]) -> i64 {
+    let mut result = 0;
+
+    let mut order_wrapped = order.to_vec();
+    order_wrapped.push(order[0]);
+
+    for (a, b) in order_wrapped.iter().tuple_windows() {
+        result += neighbors
+            .iter()
+            .filter(|n| {
+                n.persons == (a.to_string(), b.to_string())
+                    || n.persons == (b.to_string(), a.to_string())
+            })
+            .map(|p| p.happiness)
+            .sum::<i64>();
+    }
+
+    result
+}
+
+#[derive(Debug)]
+struct Neighbors {
+    pub persons: (String, String),
+    pub happiness: i64,
+}
+
+impl Neighbors {
+    fn new(persons: (String, String), happiness: i64) -> Self {
+        Self { persons, happiness }
+    }
+
+    fn parse(s: &str) -> Self {
+        let mut parts = s.split_whitespace();
+
+        let a = parts.next().unwrap().to_string();
+        let mut b = parts.next_back().unwrap().to_string();
+        b = b.chars().take(b.len() - 1).collect();
+
+        let lose_gain = parts.nth(1).unwrap();
+
+        let sign = if lose_gain == "gain" { 1 } else { -1 };
+        let amount: i64 = parts.next().unwrap().parse().unwrap();
+
+        let happiness = amount * sign;
+
+        Self::new((a, b), happiness)
+    }
+}