day02.rs

use std::fs;

pub(crate) fn day02() {
    println!("{}", part_a(fs::read_to_string("input/2016/day02/input.txt").unwrap()));
    println!("{}", part_b(fs::read_to_string("input/2016/day02/input.txt").unwrap()));
}

fn part_a(input: String) -> i32 {
    let keypad = vec! {
        vec!{1, 2, 3},
        vec!{4, 5, 6},
        vec!{7, 8, 9},
    };

    let mut r = 1;
    let mut c = 1;
    input.lines().map(|instructions| {
        for i in instructions.chars() {
            match i {
                'U' => { if r > 0 { r -= 1 } }
                'D' => { if r < 2 { r += 1 } }
                'L' => { if c > 0 { c -= 1 } }
                'R' => { if c < 2 { c += 1 } }
                _ => panic!("Unknown instruction {}", i)
            }
        }

        keypad[r][c]
    }).reduce(|a, b| a * 10 + b).unwrap()
}

fn part_b(input: String) -> String {
    let keypad = vec! {
        vec!{ ' ', ' ', '1', ' ', ' ' },
        vec!{ ' ', '2', '3', '4', ' ' },
        vec!{ '5', '6', '7', '8', '9' },
        vec!{ ' ', 'A', 'B', 'C', ' ' },
        vec!{ ' ', ' ', 'D', ' ', ' ' },
    };

    let mut ans = String::new();
    let mut r = 2;
    let mut c = 0;

    for instructions in input.lines() {
        for i in instructions.chars() {
            match i {
                'U' => { if r > 0 && keypad[r - 1][c] != ' ' { r -= 1 } }
                'D' => { if r < 4 && keypad[r + 1][c] != ' ' { r += 1 } }
                'L' => { if c > 0 && keypad[r][c - 1] != ' ' { c -= 1 } }
                'R' => { if c < 4 && keypad[r][c + 1] != ' ' { c += 1 } }
                _ => panic!("Unknown instruction {}", i)
            }
        }

        ans.push(keypad[r][c])
    }

    ans
}

#[cfg(test)]
mod day02_tests {
    use std::fs;

    use crate::y2016::day02::{part_a, part_b};

    #[test]
    fn test_works() {
        assert_eq!(1985, part_a(fs::read_to_string("input/2016/day02/test.txt").unwrap()));
        assert_eq!("5DB3", part_b(fs::read_to_string("input/2016/day02/test.txt").unwrap()));
    }

    #[test]
    fn input_works() {
        assert_eq!(92435, part_a(fs::read_to_string("input/2016/day02/input.txt").unwrap()));
        assert_eq!("C1A88", part_b(fs::read_to_string("input/2016/day02/input.txt").unwrap()));
    }
}