67 lines
1.7 KiB
Rust
67 lines
1.7 KiB
Rust
use anyhow::{anyhow, Result};
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use std::collections::HashSet;
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use std::fs::File;
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use std::io::prelude::*;
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use std::io::BufReader;
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const INPUT: &str = "input/input.txt";
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fn solve_part1(input_path: &str) -> Result<i32> {
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let file = File::open(input_path)?;
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let reader = BufReader::new(file);
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let mut prev_numbers = HashSet::new();
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for line in reader.lines() {
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let number: i32 = line?.parse()?;
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let other_half = 2020 - number;
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if prev_numbers.contains(&other_half) {
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return Ok(number * other_half);
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}
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prev_numbers.insert(number);
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}
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Err(anyhow!("Found no pair of numbers that sums to 2020"))
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}
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fn solve_part2(input_path: &str) -> Result<i32> {
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let file = File::open(input_path)?;
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let reader = BufReader::new(file);
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let mut prev_numbers = HashSet::new();
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for line in reader.lines() {
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let number: i32 = line?.parse()?;
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for prev_number in prev_numbers.iter() {
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let other_third = 2020 - prev_number - number;
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if prev_numbers.contains(&other_third) {
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return Ok(number * prev_number * other_third);
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}
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}
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prev_numbers.insert(number);
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}
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Err(anyhow!("Found no three numbers that sum to 2020"))
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}
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fn main() {
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println!("Part 1: {}", solve_part1(INPUT).unwrap());
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println!("Part 2: {}", solve_part2(INPUT).unwrap());
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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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const TEST_INPUT: &str = "input/test.txt";
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#[test]
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fn solves_part1() {
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assert_eq!(solve_part1(TEST_INPUT).unwrap(), 514579);
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}
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#[test]
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fn solves_part2() {
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assert_eq!(solve_part2(TEST_INPUT).unwrap(), 241861950);
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}
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}
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