105 lines
2.3 KiB
Rust
105 lines
2.3 KiB
Rust
use std::collections::HashSet;
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use std::fmt::Write;
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use aoc::{err, Result};
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const INPUT: &str = include_str!("../input/day01.txt");
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pub fn run() -> Result<String> {
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let mut res = String::with_capacity(128);
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writeln!(res, "part 1: {}", part1(INPUT)?)?;
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writeln!(res, "part 2: {}", part2(INPUT)?)?;
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Ok(res)
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}
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fn part1(input: &str) -> Result<i64> {
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let entries = input
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.lines()
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.map(|line| line.parse::<i64>().map_err(|e| err!("{}", e)))
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.collect::<Result<Vec<i64>>>()?;
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let (a, b) = find_2020_2_sum(&entries)?;
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Ok(a * b)
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}
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fn part2(input: &str) -> Result<i64> {
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let entries = input
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.lines()
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.map(|line| line.parse::<i64>().map_err(|e| err!("{}", e)))
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.collect::<Result<Vec<i64>>>()?;
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let (a, b, c) = find_2020_3_sum(&entries)?;
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Ok(a * b * c)
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}
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fn find_2020_2_sum(entries: &[i64]) -> Result<(i64, i64)> {
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for i in 0..entries.len() {
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for j in 0..entries.len() {
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if i == j {
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continue;
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}
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if entries[i] + entries[j] == 2020 {
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return Ok((entries[i], entries[j]));
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}
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}
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}
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Err(err!("couldn't find 2 elements that sum to 2020"))
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}
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fn find_2020_3_sum(entries: &[i64]) -> Result<(i64, i64, i64)> {
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let set: HashSet<i64> = entries.iter().copied().collect();
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for i in 0..entries.len() {
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for j in 0..entries.len() {
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if i == j {
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continue;
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}
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let a = entries[i];
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let b = entries[j];
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let c = 2020 - a - b;
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if set.contains(&c) {
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return Ok((a, b, c));
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}
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}
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}
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Err(err!("couldn't find 2 elements that sum to 2020"))
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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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static PROVIDED: &[i64] = &[1721, 979, 366, 299, 675, 1456];
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#[test]
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fn part1_provided() {
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let (a, b) = find_2020_2_sum(PROVIDED).unwrap();
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assert_eq!(a + b, 2020);
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}
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#[test]
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fn part1_real() {
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assert_eq!(part1(INPUT).unwrap(), 1014171);
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}
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#[test]
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fn part2_provided() {
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let (a, b, c) = find_2020_3_sum(PROVIDED).unwrap();
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assert_eq!(a + b + c, 2020);
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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(), 46584630);
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}
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}
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