43 lines
1.0 KiB
Rust
43 lines
1.0 KiB
Rust
use crate::prelude::*;
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pub fn solution() -> Solution {
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Solution::new(Day::new(15, 2020), part_1, part_2).with_expected(441, 10613991)
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}
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fn solve(input: &str, target: usize) -> isize {
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let mut numbers = HashMap::new();
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let mut previous_number = (0, (0, 0));
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for (index, number) in input
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.trim()
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.split(',')
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.map(str::parse::<isize>)
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.map(Result::unwrap)
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.enumerate()
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{
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numbers.insert(number, (index, index));
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previous_number = (number, (index, index));
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}
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for index in numbers.len()..target {
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let next_num = previous_number.1 .1 - previous_number.1 .0;
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let num = numbers
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.entry(next_num as isize)
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.or_insert_with(|| (index, index));
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num.0 = num.1;
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num.1 = index;
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previous_number = (next_num as isize, *num);
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}
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*numbers.iter().max_by(|a, b| a.1 .1.cmp(&b.1 .1)).unwrap().0
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}
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fn part_1(input: &str) -> Result<String> {
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Ok(solve(input, 2020).to_string())
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}
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fn part_2(input: &str) -> Result<String> {
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Ok(solve(input, 30000000).to_string())
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}
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