aoc/year2024/
day03.rs

1//! # Mull It Over
2//!
3//! Solves both parts simultaneously using a custom parser instead of
4//! [regex](https://en.wikipedia.org/wiki/Regular_expression).
5use crate::util::parse::*;
6
7type Input = (u32, u32);
8
9pub fn parse(input: &str) -> Input {
10    let memory = input.as_bytes();
11    let mut index = 0;
12    let mut enabled = true;
13    let mut part_one = 0;
14    let mut part_two = 0;
15
16    while index < memory.len() {
17        // Skip junk characters
18        if memory[index] != b'm' && memory[index] != b'd' {
19            index += 1;
20            continue;
21        }
22
23        // Check possible prefixes
24        if memory[index..].starts_with(b"mul(") {
25            index += 4;
26        } else if memory[index..].starts_with(b"do()") {
27            index += 4;
28            enabled = true;
29            continue;
30        } else if memory[index..].starts_with(b"don't()") {
31            index += 7;
32            enabled = false;
33            continue;
34        } else {
35            index += 1;
36            continue;
37        }
38
39        // Parse first number
40        let first = parse_number(memory, &mut index);
41
42        // First delimiter
43        if memory[index] != b',' {
44            continue;
45        }
46        index += 1;
47
48        // Parse second number
49        let second = parse_number(memory, &mut index);
50
51        // Second delimiter
52        if memory[index] != b')' {
53            continue;
54        }
55        index += 1;
56
57        // Multiply
58        let product = first * second;
59        part_one += product;
60        part_two += if enabled { product } else { 0 };
61    }
62
63    (part_one, part_two)
64}
65
66fn parse_number(memory: &[u8], index: &mut usize) -> u32 {
67    let mut number = 0;
68    while memory[*index].is_ascii_digit() {
69        number = 10 * number + memory[*index].to_decimal() as u32;
70        *index += 1;
71    }
72    number
73}
74
75pub fn part1(input: &Input) -> u32 {
76    input.0
77}
78
79pub fn part2(input: &Input) -> u32 {
80    input.1
81}
aoc/year2024/day03.rs

aoc/year2024/
day03.rs
