Solution for Flip Flop 2025 Day 2

day02.rs

use std::time::Instant;

use cached::proc_macro::cached;
use itertools::Itertools;

const INPUT: &str = include_str!("inputs/day02.txt");

fn parse(input: &str) -> impl Iterator<Item = char> {
    input.trim().chars()
}

fn p1(input: &str) -> isize {
    parse(input)
        .scan(0isize, |acc, c| {
            *acc += match c {
                '^' => 1,
                _ => -1,
            };
            Some(*acc)
        })
        .max()
        .unwrap()
}

fn p2(input: &str) -> isize {
    parse(input)
        .scan((0isize, true, 0), |(acc, up, count), c| {
            // Update count.
            *count = match (c, *up) {
                ('^', true) => *count + 1,
                ('v', false) => *count + 1,
                _ => {
                    *up = !*up;
                    1
                }
            };
            *acc += match c {
                '^' => *count,
                _ => -*count,
            };
            Some(*acc)
        })
        .max()
        .unwrap()
}

#[cached]
fn fib(n: isize) -> isize {
    if n == 0 {
        0
    } else if n == 1 {
        1
    } else {
        fib(n - 1) + fib(n - 2)
    }
}

fn p3(input: &str) -> isize {
    parse(input)
        .chunk_by(|c| *c)
        .into_iter()
        .map(|(k, g)| (k, fib(g.count() as isize)))
        .scan(0isize, |acc, (k, v)| {
            *acc += match k {
                '^' => v,
                _ => -v,
            };
            Some(*acc)
        })
        .max()
        .unwrap()
}

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);

    let now = Instant::now();
    let solution = p3(INPUT);
    println!("p3 {:?} {}", now.elapsed(), solution);
}