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Death to imperative programming!

This commit is contained in:
kageru 2021-12-06 14:09:46 +01:00
parent fcab7acc74
commit 728b95b9e1
1 changed files with 7 additions and 10 deletions
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17
2021/src/bin/day06.rs
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@ -1,10 +1,11 @@
#![feature(test)]
extern crate test;
use aoc2021::common::*;
use std::iter;
const DAY: usize = 6;
const FERTILITY_CYCLE: usize = 7;
const DAYS_TO_FERTILITY: usize = 2;
const INITIAL_DELAY: usize = FERTILITY_CYCLE + 2;
type Parsed = Vec<usize>;
fn parse_input(raw: &str) -> Parsed {
@ -12,17 +13,13 @@ fn parse_input(raw: &str) -> Parsed {
}
fn simulate<const LIMIT: usize>(parsed: &Parsed) -> usize {
let next_fertile_day = |day: &usize| Some(day + FERTILITY_CYCLE).filter(|n| n < &LIMIT);
let mut fish_from_day = [1; LIMIT];
for i in (0..LIMIT).rev() {
let mut next_child = i + FERTILITY_CYCLE + DAYS_TO_FERTILITY;
while next_child < LIMIT {
fish_from_day[i] += fish_from_day[next_child];
next_child += FERTILITY_CYCLE;
}
for i in (0..LIMIT - INITIAL_DELAY).rev() {
fish_from_day[i] += iter::successors(Some(i + INITIAL_DELAY), next_fertile_day).map(|n| fish_from_day[n]).sum::<usize>()
}
let adult_from_day: Vec<usize> = (0..FERTILITY_CYCLE)
.map(|i| std::iter::successors(Some(i), |i| Some(i + FERTILITY_CYCLE).filter(|i| i < &LIMIT)).map(|i| fish_from_day[i]).sum())
.collect();
let adult_from_day: Vec<usize> =
(0..FERTILITY_CYCLE).map(|i| iter::successors(Some(i), next_fertile_day).map(|i| fish_from_day[i]).sum()).collect();
parsed.iter().map(|&i| 1 + adult_from_day[i]).sum()
}