Add D16P2
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@ -2,19 +2,59 @@ use std::io::{stdin, BufRead};
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use std::iter::*;
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#[rustfmt::skip]
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fn read_input() -> Vec<i16> {
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fn read_input() -> Vec<i32> {
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stdin().lock().lines().next().unwrap().unwrap().chars().map(|c| c.to_string().parse().unwrap()).collect()
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}
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#[rustfmt::skip]
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fn main() {
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let mut last_phase = read_input();
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//let mut last_phase: Vec<i16> = "80871224585914546619083218645595".chars().map(|c| c.to_string().parse().unwrap()).collect();
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fn part1(mut last_phase: Vec<i32>) -> String {
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for _ in 0..100 {
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last_phase = (1..=last_phase.len()).map(|i| {
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let mut pattern = [0i16, 1, 0, -1].iter().flat_map(|x| repeat(x).take(i)).cycle().skip(1);
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last_phase.iter().map(|x| x*pattern.next().unwrap()).sum::<i16>().abs() % 10
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let mut pattern = [0i32, 1, 0, -1].iter().flat_map(|x| repeat(x).take(i)).cycle().skip(1);
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last_phase.iter().map(|x| x*pattern.next().unwrap()).sum::<i32>().abs() % 10
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}).collect();
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}
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println!("Part 1: {}", last_phase.iter().take(8).map(|n| n.to_string()).collect::<String>());
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last_phase.iter().take(8).map(|n| n.to_string()).collect::<String>()
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}
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/**
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* The outputs after each phase are related in a way that I can’t really explain.
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* They are essentially a summed-area table, but built starting with the last element.
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* However, this only works for the second half of the output. The rest seem to be random?
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*
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* The examples show this quite clearly:
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* Input signal: 12345678 (let’s call this `input`)
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* After 1 phase: 48226158 (`output`)
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* We can build the state after 1 phase right to left.
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* ```
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* output[7] = input[7..8].iter().sum() % 10; // 8
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* output[6] = input[6..8].iter().sum() % 10; // 15 % 10 == 5
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* output[5] = input[5..8].iter().sum() % 10; // 21 % 10 == 1
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* output[4] = input[4..8].iter().sum() % 10; // 26 % 10 == 6
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* ```
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* Which is exactly the output sequence.
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* This pattern only holds true for the second half of the array,
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* but the offset always seems to be high enough for that.
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*
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* Because all input elements only affect outputs with lower indices,
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* we can also drop all elements before the output starts.
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*/
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#[rustfmt::skip]
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fn part2(input: Vec<i32>) -> String {
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let offset: usize = input.iter().take(7).map(|n| n.to_string()).collect::<String>().parse().unwrap();
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let mut p2 = input.repeat(10_000).split_off(offset);
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for _ in 0..100 {
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let mut s = 0;
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for i in (0..p2.len()).rev() {
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s += p2[i];
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p2[i] = s % 10;
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}
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}
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p2.iter().take(8).map(|n| n.to_string()).collect::<String>()
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}
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fn main() {
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let input = read_input();
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println!("Part 1: {}", part1(input.clone()));
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println!("Part 2: {}", part2(input));
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}
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