diff --git a/2017/rust/src/day_06.rs b/2017/rust/src/day_06.rs
new file mode 100644
index 0000000..e1ddb9d
--- /dev/null
+++ b/2017/rust/src/day_06.rs
@@ -0,0 +1,69 @@
+use std::collections::HashSet;
+use failure::*;
+
+pub fn solve(input: &str) -> Result<String, Error> {
+ let banks: Vec<_> = input
+ .split_whitespace()
+ .map(str::parse)
+ .collect::<Result<_, _>>()?;
+
+ let mut reallocation = Reallocation { banks: banks.clone() };
+ let cycles = unique_cycles(reallocation);
+
+ reallocation = Reallocation { banks };
+ Ok((unique_cycles(reallocation.skip(cycles - 1)) - 1).to_string())
+}
+
+fn unique_cycles<R: Iterator<Item=Vec<usize>>>(reallocation: R) -> usize {
+ let mut seen = HashSet::new();
+ for (i, banks) in reallocation.enumerate() {
+ if seen.contains(&banks) {
+ return i + 1;
+ }
+
+ seen.insert(banks.clone());
+ }
+ unreachable!();
+}
+
+#[test]
+fn test_part_one() {
+ let reallocation = Reallocation { banks: vec![0, 2, 7, 0] };
+ assert_eq!(unique_cycles(reallocation), 5);
+}
+
+struct Reallocation {
+ banks: Vec<usize>,
+}
+
+impl Iterator for Reallocation {
+ type Item = Vec<usize>;
+
+ fn next(&mut self) -> Option<Self::Item> {
+ let banks = self.banks.clone();
+ let mut banks: Vec<_> = banks.iter().enumerate().collect();
+ banks.reverse();
+ let (start, max) = banks
+ .iter()
+ .max_by_key(|&&(_, x)| x)
+ .map(|&(i, x)| (i, x.clone()))?;
+
+ let len = self.banks.len();
+ self.banks[start] = 0;
+ for i in 1..=max {
+ self.banks[(start + i) % len] += 1;
+ }
+
+ Some(self.banks.clone())
+ }
+}
+
+#[test]
+fn test_reallocation() {
+ let mut r = Reallocation {
+ banks: vec![0, 2, 7, 0],
+ };
+ assert_eq!(r.next(), Some(vec![2, 4, 1, 2]));
+ assert_eq!(r.next(), Some(vec![3, 1, 2, 3]));
+ assert_eq!(r.next(), Some(vec![0, 2, 3, 4]));
+}
diff --git a/2017/rust/src/day_15.rs b/2017/rust/src/day_15.rs
index c429d43..e6a9544 100644
--- a/2017/rust/src/day_15.rs
+++ b/2017/rust/src/day_15.rs
@@ -1,6 +1,7 @@
use failure::*;
use regex::Regex;
+#[allow(dead_code)]
pub fn solve(input: &str) -> Result<String, Error> {
let re: Regex = Regex::new(r"\d+")?;
let matches: Vec<_> = re.find_iter(input)
diff --git a/2017/rust/src/main.rs b/2017/rust/src/main.rs
index ff8c10f..6eb8141 100644
--- a/2017/rust/src/main.rs
+++ b/2017/rust/src/main.rs
@@ -1,4 +1,4 @@
-#![feature(conservative_impl_trait)]
+#![feature(conservative_impl_trait, inclusive_range_syntax)]
extern crate failure;
#[macro_use]
@@ -14,6 +14,7 @@ mod day_02;
mod day_03;
mod day_04;
mod day_05;
+mod day_06;
mod day_15;
fn main() {
@@ -26,7 +27,7 @@ fn run() -> Result<(), Error> {
let mut input = String::new();
io::stdin().read_to_string(&mut input)?;
- let solution = day_15::solve(&input)?;
+ let solution = day_06::solve(&input)?;
println!("{}", solution);
Ok(())