2019: day06: part 2
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@ -1,4 +1,5 @@
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use std::collections::HashMap;
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use std::iter;
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use aoc::err;
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use aoc::Result;
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@ -7,6 +8,7 @@ const INPUT: &str = include_str!("../input/day06.txt");
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pub fn run() -> Result<()> {
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println!("part 1: {}", part1(INPUT)?);
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println!("part 2: {}", part2(INPUT)?);
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Ok(())
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}
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@ -48,6 +50,33 @@ fn part1(input: &str) -> Result<u64> {
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.sum())
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}
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fn part2(input: &str) -> Result<usize> {
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let orbits = input
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.lines()
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.map(|line| line.trim_end())
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.map(|line| {
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let paren = line
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.find(')')
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.ok_or_else(|| err!("couldn't find `)` in line: {}", line))?;
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Ok((line[paren + 1..].to_string(), line[..paren].to_string()))
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})
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.collect::<Result<HashMap<String, String>>>()?;
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let succ = |key: &String| orbits.get(key).map(|val| val.clone());
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let you_path = iter::successors(Some("YOU".to_string()), succ).collect::<Vec<_>>();
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let santa_path = iter::successors(Some("SAN".to_string()), succ).collect::<Vec<_>>();
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let common = you_path
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.iter()
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.rev()
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.zip(santa_path.iter().rev())
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.filter(|(x, y)| x == y)
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.count();
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Ok(you_path.len() - common + santa_path.len() - common - 2)
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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@ -63,6 +92,21 @@ D)I
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E)J
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J)K
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K)L
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";
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const PROVIDED2: &str = "COM)B
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B)C
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C)D
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D)E
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E)F
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B)G
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G)H
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D)I
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E)J
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J)K
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K)L
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K)YOU
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I)SAN
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";
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#[test]
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@ -74,4 +118,14 @@ K)L
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fn part1_real() {
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assert_eq!(part1(INPUT).unwrap(), 140608);
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}
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#[test]
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fn part2_provided() {
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assert_eq!(part2(PROVIDED2).unwrap(), 4);
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}
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#[test]
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fn part2_real() {
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assert_eq!(part2(INPUT).unwrap(), 337);
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}
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}
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