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use anyhow::anyhow;
use std::fs::File;
use std::io::prelude::*;
use std::io::BufReader;
const PART_2: bool = true;
fn day01(is_part2: bool, numbers: &Vec<i64>) -> Result<String, anyhow::Error> {
// println!("{:?}", numbers);
for n1 in numbers.iter() {
for n2 in numbers.iter() {
if is_part2 {
for n3 in numbers.iter() {
if n1 + n2 + n3 == 2020 {
return Ok((n1 * n2 * n3).to_string());
}
}
} else {
if n1 + n2 == 2020 {
return Ok((n1 * n2).to_string());
}
}
}
}
Err(anyhow!("no solution found"))
}
fn parse(filename: &str) -> Result<Vec<i64>, anyhow::Error> {
let f = File::open(filename)?;
let mut reader = BufReader::new(f);
let mut values = Vec::<i64>::new();
let mut line = String::new();
loop {
line.clear();
reader.read_line(&mut line)?;
let trimmed_line = line.trim();
if trimmed_line.is_empty() {
break;
}
values.push(trimmed_line.parse()?);
}
Ok(values)
}
fn main() -> anyhow::Result<()> {
let args: Vec<String> = std::env::args().collect();
// println!("{:?}", args);
if args.len() != 2 {
return Err(anyhow!("usage: day01 input_file"));
}
let filename = args.into_iter().skip(1).next().expect("args len == 1");
let numbers = parse(&filename)?;
println!("{}", day01(PART_2, &numbers)?);
Ok(())
}
#[cfg(test)]
mod tests {
use super::day01;
#[test]
fn test_part1() {
let vec = vec![1721, 979, 366, 299, 675, 1456];
let result = day01(false, &vec).unwrap();
assert_eq!(result, 514579.to_string());
}
#[test]
fn test_part2() {
let vec = vec![1721, 979, 366, 299, 675, 1456];
let result = day01(true, &vec).unwrap();
assert_eq!(result, 241861950.to_string());
}
}
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