42 lines
1.0 KiB
Rust
42 lines
1.0 KiB
Rust
use itertools::Itertools;
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use std::io::BufRead;
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fn main() {
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let input: Vec<usize> = std::io::stdin()
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.lock()
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.lines()
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.filter_map(|l| l.unwrap().parse().ok())
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.collect();
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let p1 = input
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.iter()
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.tuple_combinations()
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.filter(|(&a, &b)| a + b == 2020)
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.map(|(a, b)| a * b)
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.next()
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.unwrap();
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println!("Part 1: {}", p1);
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/*
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smol-brain, n³ solution:
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let p2 = input
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.tuple_combinations()
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.filter(|(&a, &b, &c)| a + b + c == 2020)
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.map(|(a, b, c)| a * b * c)
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.next()
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.unwrap();
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println!("Part 2: {}", p2);
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*/
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// Ascended n² solution (thanks to Lypheo)
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let mut p2_table = vec![None; 2020];
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for (&a, &b) in input.iter().tuple_combinations() {
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if a + b < 2020 {
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p2_table[a + b] = Some((a, b))
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}
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}
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let (a, b) = input
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.iter()
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.filter_map(|x| p2_table[2020 - x])
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.next()
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.unwrap();
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println!("Part 2: {}", a * b * (2020 - a - b));
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}
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