From 2ca2d974a079e3d62da38169d8af6af33f45ab27 Mon Sep 17 00:00:00 2001
From: June McEnroe <june@causal.agency>
Date: Tue, 20 Dec 2016 20:16:07 -0500
Subject: Day 19

---
 src/bin/day19.rs | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)
 create mode 100644 src/bin/day19.rs

(limited to 'src')

diff --git a/src/bin/day19.rs b/src/bin/day19.rs
new file mode 100644
index 0000000..89013b3
--- /dev/null
+++ b/src/bin/day19.rs
@@ -0,0 +1,37 @@
+use std::io::{self, Read};
+
+#[derive(Clone, Copy)]
+struct Elf {
+    gifts: usize,
+    next: usize,
+}
+
+fn solve(count: usize) -> usize {
+    let mut circle: Vec<Elf> = (0..count).map(|i| Elf { gifts: 1, next: i + 1 }).collect();
+    circle.last_mut().unwrap().next = 0;
+
+    let mut index = 0;
+
+    while circle[index].gifts < count {
+        let next = circle[index].next;
+        circle[index].gifts += circle[next].gifts;
+        circle[next].gifts = 0;
+        circle[index].next = circle[next].next;
+
+        index = circle[index].next;
+    }
+
+    index + 1
+}
+
+fn main() {
+    let mut input = String::new();
+    io::stdin().read_to_string(&mut input).unwrap();
+
+    println!("Part 1: {}", solve(input.trim().parse().unwrap()));
+}
+
+#[test]
+fn part1() {
+    assert_eq!(3, solve(5));
+}
-- 
cgit 1.4.1