advent-of-code-2017/day_5/src/lib.rs

pub mod day_5 {
    use std::convert::TryFrom;

    pub fn input() -> Vec<i32> {
        let input = include_str!("../input.txt");
        input
            .lines()
            .map(|l| {
                l.parse()
                    .unwrap_or_else(|_| panic!("{} wasn't a valid u32", l))
            })
            .collect::<Vec<i32>>()
    }

    pub fn part_1(v: &mut Vec<i32>) -> u32 {
        let mut count = 0;
        let mut index: usize = 0;
        while index < v.len() {
            let bounce = v[index];
            v[index] = bounce + 1;
            let test = i32::try_from(index).unwrap() + bounce;
            if test < 0 {
                return count;
            }
            index = usize::try_from(test).unwrap();
            count += 1;
        }
        count
    }

    pub fn part_2(v: &mut Vec<i32>) -> u32 {
        let mut count = 0;
        let mut index: usize = 0;
        while index < v.len() {
            let bounce = v[index];
            if bounce >= 3 {
                v[index] = bounce - 1;
            } else {
                v[index] = bounce + 1;
            }
            let test = i32::try_from(index).unwrap() + bounce;
            if test < 0 {
                return count;
            }
            index = usize::try_from(test).unwrap();
            count += 1;
        }
        count
    }
}

#[cfg(test)]
mod tests {
    use super::day_5::*;

    #[test]
    fn part1_known() {
        assert_eq!(part_1(&mut vec![0, 3, 0, 1, -3]), 5);
    }

    #[test]
    fn part2_known() {
        assert_eq!(part_2(&mut vec![0, 3, 0, 1, -3]), 10);
    }

    #[test]
    fn test_day_5() {
        let input = input();
        assert_eq!(part_1(&mut input.clone()), 391540);
        let mut input = input;
        assert_eq!(part_2(&mut input), 30513679);
    }
}