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#![allow(dead_code)]
use std::fs;
use std::collections::HashSet;
fn read_file(file: &str) -> String {
fs::read_to_string(file).unwrap()
}
fn read_numbers(file: &str) -> Vec<i32> {
read_file(file).split('\n')
.filter(|x| !x.is_empty())
.map(|x| x.parse::<i32>().unwrap())
.collect()
}
fn find_pair_with_sum(numbers: &HashSet<i32>, goal: i32) -> Option<(i32, i32)> {
for i in numbers {
if numbers.contains(&(goal - i)) {
return Some((*i, goal - i));
}
}
None
}
fn day1() {
let input = read_numbers("input01");
let mut numbers = HashSet::new();
for i in &input {
numbers.insert(*i);
}
let (x, y) = match find_pair_with_sum(&numbers, 2020) {
Some(pair) => pair,
None => panic!("nothing found"),
};
println!("1a: {}", x * y);
for i in &numbers {
let (x, y) = match find_pair_with_sum(&numbers, 2020 - i) {
Some(pair) => pair,
None => continue,
};
println!("1b: {}", i * x * y);
break;
}
}
fn main() {
day1();
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_day1() {
let input = [1721, 979, 366, 299, 675, 1456];
let mut numbers = HashSet::new();
for i in &input {
numbers.insert(*i);
}
let (x, y) = find_pair_with_sum(&numbers, 2020).unwrap();
assert_eq!(x * y, 514579);
for i in &numbers {
let (x, y) = match find_pair_with_sum(&numbers, 2020 - i) {
Some(pair) => pair,
None => continue,
};
assert_eq!(i + x + y, 2020);
assert_eq!(i * x * y, 241861950);
break;
}
}
}
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