57 lines
1.2 KiB
Rust
57 lines
1.2 KiB
Rust
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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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Ok(res)
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}
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fn part1(input: &str) -> Result<u64> {
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let entries = input
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.lines()
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.map(|line| line.parse::<u64>().map_err(|e| err!("{}", e)))
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.collect::<Result<Vec<u64>>>()?;
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let (a, b) = find_2020_sum(&entries)?;
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Ok(a * b)
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}
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fn find_2020_sum(entries: &[u64]) -> Result<(u64, u64)> {
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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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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn part1_provided() {
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let (a, b) = find_2020_sum(&vec![1721, 979, 366, 299, 675, 1456]).unwrap();
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assert_eq!(a, 1721);
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assert_eq!(b, 299);
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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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}
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