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77 lines
1.8 KiB
77 lines
1.8 KiB
use std::collections::HashSet;
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use failure::*;
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#[allow(dead_code)]
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pub fn solve(input: &str) -> Result<String, Error> {
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let banks: Vec<_> = input
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.split_whitespace()
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.map(str::parse)
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.collect::<Result<_, _>>()?;
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let mut reallocation = Reallocation {
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banks: banks.clone(),
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};
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let cycles = unique_cycles(reallocation);
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reallocation = Reallocation { banks };
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Ok((unique_cycles(reallocation.skip(cycles - 1)) - 1).to_string())
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}
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#[allow(dead_code)]
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fn unique_cycles<R: Iterator<Item = Vec<usize>>>(reallocation: R) -> usize {
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let mut seen = HashSet::new();
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for (i, banks) in reallocation.enumerate() {
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if seen.contains(&banks) {
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return i + 1;
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}
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seen.insert(banks.clone());
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}
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unreachable!();
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}
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#[test]
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fn test_part_one() {
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let reallocation = Reallocation {
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banks: vec![0, 2, 7, 0],
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};
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assert_eq!(unique_cycles(reallocation), 5);
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}
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#[allow(dead_code)]
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struct Reallocation {
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banks: Vec<usize>,
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}
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impl Iterator for Reallocation {
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type Item = Vec<usize>;
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fn next(&mut self) -> Option<Self::Item> {
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let banks = self.banks.clone();
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let mut banks: Vec<_> = banks.iter().enumerate().collect();
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banks.reverse();
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let (start, max) = banks
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.iter()
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.max_by_key(|&&(_, x)| x)
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.map(|&(i, x)| (i, *x))?;
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let len = self.banks.len();
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self.banks[start] = 0;
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for i in 1..=max {
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self.banks[(start + i) % len] += 1;
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}
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Some(self.banks.clone())
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}
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}
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#[test]
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fn test_reallocation() {
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let mut r = Reallocation {
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banks: vec![0, 2, 7, 0],
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};
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assert_eq!(r.next(), Some(vec![2, 4, 1, 2]));
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assert_eq!(r.next(), Some(vec![3, 1, 2, 3]));
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assert_eq!(r.next(), Some(vec![0, 2, 3, 4]));
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}
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