advent_of_code/year2020/
day02.rs

1use crate::input::Input;
2
3pub fn solve(input: &Input) -> Result<u32, String> {
4    let mut valid_passwords = 0;
5
6    for (line_index, line) in input.text.lines().enumerate() {
7        let on_error = || {
8            format!(
9                "Line {}: Invalid format - expected '$START-$END $CHAR: $PASSWORD'",
10                line_index + 1
11            )
12        };
13
14        let (password_policy_str, password) = line.split_once(": ").ok_or_else(on_error)?;
15
16        let mut policy_parts = password_policy_str.split(' ');
17        let mut occurrences_parts = policy_parts.next().ok_or_else(on_error)?.split('-');
18        let policy_char = policy_parts
19            .next()
20            .ok_or_else(on_error)?
21            .chars()
22            .next()
23            .ok_or_else(on_error)?;
24
25        let policy_start = occurrences_parts
26            .next()
27            .ok_or_else(on_error)?
28            .parse::<usize>()
29            .map_err(|_| on_error())?;
30        let policy_end = occurrences_parts
31            .next()
32            .ok_or_else(on_error)?
33            .parse::<usize>()
34            .map_err(|_| on_error())?;
35
36        if input.is_part_one() {
37            let actual_occurrences = password.chars().filter(|&c| c == policy_char).count();
38            if (policy_start..=policy_end).contains(&actual_occurrences) {
39                valid_passwords += 1;
40            }
41        } else {
42            let correct_count = password
43                .chars()
44                .enumerate()
45                .filter(|(index, c)| {
46                    (policy_start == index + 1 || policy_end == index + 1) && *c == policy_char
47                })
48                .count();
49            if correct_count == 1 {
50                valid_passwords += 1;
51            }
52        }
53    }
54    Ok(valid_passwords)
55}
56
57#[test]
58pub fn tests() {
59    test_part_one!("1-3 a: abcde\n1-3 b: cdefg\n2-9 c: ccccccccc" => 2);
60    test_part_two!("1-3 a: abcde\n1-3 b: cdefg\n2-9 c: ccccccccc" => 1);
61
62    test_part_one_error!("1- b: asdf" => "Line 1: Invalid format - expected '$START-$END $CHAR: $PASSWORD'");
63    test_part_two_error!("1-3 a: asdf\nhi\n" => "Line 2: Invalid format - expected '$START-$END $CHAR: $PASSWORD'");
64
65    let real_input = include_str!("day02_input.txt");
66    test_part_one!(real_input => 636);
67    test_part_two!(real_input => 588);
68}
advent_of_code/year2020/day02.rs

advent_of_code/year2020/
day02.rs
