Solution for Advent of Code 2017 Day 6

day06.rs

use std::time::Instant;

use rustc_hash::{FxHashMap, FxHashSet};

const INPUT: &str = include_str!("inputs/day06.txt");

fn parse(input: &str) -> Vec<usize> {
    input
        .split_whitespace()
        .map(|v| v.parse::<usize>().unwrap())
        .collect()
}

fn p1(input: &str) -> usize {
    let mut bank = parse(input);
    let mut seen = FxHashSet::default();
    let mut iterations = 0;

    loop {
        iterations += 1;

        // Find the largest values (lower index preference).
        let (i, &v) = bank
            .iter()
            .enumerate()
            .max_by(|(i1, v1), (i2, v2)| v1.cmp(v2).then(i2.cmp(i1)))
            .unwrap();

        // Redistribute.
        bank[i] = 0;
        for n in i + 1..i + 1 + v {
            let n = n % bank.len();
            bank[n] += 1;
        }

        // Check for seen.
        if !seen.insert(bank.clone()) {
            return iterations;
        }
    }
}

fn p2(input: &str) -> usize {
    let mut bank = parse(input);
    let mut seen = FxHashMap::default();
    let mut iterations: usize = 0;

    loop {
        iterations += 1;

        // Find the largest values (lower index preference).
        let (i, &v) = bank
            .iter()
            .enumerate()
            .max_by(|(i1, v1), (i2, v2)| v1.cmp(v2).then(i2.cmp(i1)))
            .unwrap();

        // Redistribute.
        bank[i] = 0;
        for n in i + 1..i + 1 + v {
            let n = n % bank.len();
            bank[n] += 1;
        }

        // Check for seen.
        if let Some(original) = seen.get(&bank.clone()) {
            return iterations - original;
        } else {
            seen.insert(bank.clone(), iterations);
        }
    }
}

fn main() {
    let now = Instant::now();
    let solution = p1(INPUT);
    println!("p1 {:?} {}", now.elapsed(), solution);

    let now = Instant::now();
    let solution = p2(INPUT);
    println!("p2 {:?} {}", now.elapsed(), solution);
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_p1() {
        let input = "0 2 7 0";
        assert_eq!(p1(input), 5);
    }

    #[test]
    fn test_p2() {
        let input = "0 2 7 0";
        assert_eq!(p2(input), 4);
    }
}