src/bin/day2.rs


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static DAY: u8 = 2;

fn main() {
    let input = advent::read_lines(DAY);
    println!("{DAY}a: {}", safe_reports(&input));
    println!("{DAY}b: {}", 0);
}

fn is_report_safe(report: &[i32]) -> bool {
    let increasing = report[1] - report[0] > 0;
    for number in report.iter().as_slice().windows(2) {
        let diff = number[1] - number[0];
        if diff.abs() < 1 || diff.abs() > 3 {
            return false;
        }
        if (diff > 0) != increasing {
            return false;
        }
    }
    true
}

fn safe_reports(input: &[String]) -> usize {
    let mut reports = Vec::new();
    for line in input {
        let numbers = line.split(" ")
                          .map(|x| x.parse::<i32>().unwrap())
                          .collect::<Vec<_>>();
        reports.push(numbers);
    }
    reports.iter()
           .filter(|x| is_report_safe(x))
           .count()
}

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

    #[test]
    fn test() {
        let input = [
            "7 6 4 2 1",
            "1 2 7 8 9",
            "9 7 6 2 1",
            "1 3 2 4 5",
            "8 6 4 4 1",
            "1 3 6 7 9",
        ].iter().map(|&x| String::from(x)).collect::<Vec<_>>();
        assert_eq!(safe_reports(&input), 2);
    }
}