Day 10

1 files changed, 38 insertions, 0 deletions

diff --git a/2017/src/bin/day10.rs b/2017/src/bin/day10.rs
new file mode 100644
index 0000000..af90961
--- /dev/null
+++ b/2017/src/bin/day10.rs
@@ -0,0 +1,38 @@
+use std::io::{self, Read};
+
+fn reverse(ring: &mut Vec<u32>, index: usize, len: usize) {
+    for i in 0..(len / 2) {
+        let a = (index + i) % ring.len();
+        let b = (index + len - 1 - i) % ring.len();
+        let x = ring[a];
+        ring[a] = ring[b];
+        ring[b] = x;
+    }
+}
+
+fn solve1(size: u32, input: &str) -> u32 {
+    let mut ring: Vec<_> = (0..size).collect();
+    let mut index = 0;
+    let mut skip = 0;
+
+    for len in input.split(',').map(str::parse).map(Result::unwrap) {
+        reverse(&mut ring, index, len);
+        index += len + skip;
+        index %= ring.len();
+        skip += 1;
+    }
+
+    ring[0] * ring[1]
+}
+
+fn main() {
+    let mut input = String::new();
+    io::stdin().read_to_string(&mut input).unwrap();
+
+    println!("Part 1: {}", solve1(256, input.trim()));
+}
+
+#[test]
+fn part1() {
+    assert_eq!(12, solve1(5, "3,4,1,5"));
+}