advent-of-code/aoc2019/src/day06.rs

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use std::collections::HashMap;
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use std::collections::HashSet;
use std::fmt::Write;
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use std::iter;
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use anyhow::{Context, Result};
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const INPUT: &str = include_str!("../input/day06.txt");
pub fn run() -> Result<String> {
let mut res = String::with_capacity(128);
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writeln!(res, "part 1: {}", part1(INPUT)?)?;
writeln!(res, "part 2: {}", part2(INPUT)?)?;
Ok(res)
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}
fn count_orbits(
key: &str,
orbits: &HashMap<String, String>,
cache: &mut HashMap<String, u64>,
) -> u64 {
match cache.get(key) {
Some(val) => *val,
None => {
let val = match orbits.get(key) {
Some(parent) => count_orbits(parent, orbits, cache) + 1,
None => 0,
};
cache.insert(key.to_string(), val);
val
}
}
}
fn part1(input: &str) -> Result<u64> {
let orbits = input
.lines()
.map(str::trim_end)
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.map(|line| {
let paren = line
.find(')')
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.with_context(|| format!("couldn't find `)` in line: {}", line))?;
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Ok((line[paren + 1..].to_string(), line[..paren].to_string()))
})
.collect::<Result<HashMap<String, String>>>()?;
let mut cache = HashMap::new();
Ok(orbits
.keys()
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.map(|k| count_orbits(k, &orbits, &mut cache))
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.sum())
}
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fn part2(input: &str) -> Result<usize> {
let orbits = input
.lines()
.map(str::trim_end)
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.map(|line| {
let paren = line
.find(')')
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.with_context(|| format!("couldn't find `)` in line: {}", line))?;
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Ok((line[paren + 1..].to_string(), line[..paren].to_string()))
})
.collect::<Result<HashMap<String, String>>>()?;
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let succ = |key: &String| orbits.get(key).cloned();
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let you_path = iter::successors(Some("YOU".to_string()), succ).collect::<HashSet<_>>();
let santa_path = iter::successors(Some("SAN".to_string()), succ).collect::<HashSet<_>>();
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Ok(you_path.symmetric_difference(&santa_path).count() - 2)
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}
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#[cfg(test)]
mod tests {
use super::*;
const PROVIDED1: &str = "COM)B
B)C
C)D
D)E
E)F
B)G
G)H
D)I
E)J
J)K
K)L
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";
const PROVIDED2: &str = "COM)B
B)C
C)D
D)E
E)F
B)G
G)H
D)I
E)J
J)K
K)L
K)YOU
I)SAN
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";
#[test]
fn part1_provided() {
assert_eq!(part1(PROVIDED1).unwrap(), 42);
}
#[test]
fn part1_real() {
assert_eq!(part1(INPUT).unwrap(), 140608);
}
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#[test]
fn part2_provided() {
assert_eq!(part2(PROVIDED2).unwrap(), 4);
}
#[test]
fn part2_real() {
assert_eq!(part2(INPUT).unwrap(), 337);
}
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}