Advent of Code day 5

day5.rs

#![feature(plugin)]
#![plugin(regex_macros)]
extern crate regex;

use std::fs::File;
use std::io::BufReader;
use std::io::BufRead;


fn passes_rule_1(s: &str) -> bool {
    let three_vowels = regex!("[aeiou].*[aeiou].*[aeiou]");
    let bad_strings = regex!("ab|cd|pq|xy");

    if bad_strings.is_match(s) {
        return false;
    }
    if !three_vowels.is_match(s) {
        return false;
    }

    // Look for two letters in a row.
    // Rust's Regex package doesn't support backreferences so we do this the old-fashioned way.
    let mut prev_char = '\0';
    for c in s.chars() {
        if prev_char != '\0' && c == prev_char { 
            return true;
        }
        prev_char = c;
    }

    false
}

fn passes_rule_2(s: &str) -> bool {
    // Look for a pair of letters that appear twice in the string (no overlaps)
    // Rust's Regex package doesn't support backreferences so we do this the old-fashioned way.
    let mut prev_char = '\0';
    let mut found = false;
    for (i, c) in s.chars().enumerate() {
        if prev_char == '\0' {
            prev_char = c;
            continue;
        }

        let pair = prev_char.to_string() + &c.to_string();
        if s[i+1..].contains(&pair) {
            found = true;
            break;
        }
        prev_char = c;
    }
    if !found {
        return false;
    }

    // Look for two letters that repeat, with one letter between them
    // Rust's Regex package doesn't support backreferences so we do this the old-fashioned way.
    let mut prev_char = '\0';
    let mut prev_prev_char = '\0';
    for c in s.chars() {
        if c == prev_prev_char {
            return true
        }

        if prev_char != '\0' {
            prev_prev_char = prev_char
        }
        prev_char = c;
    }

    false
}

fn main() {
    let input_fname = "day5_input.txt";
    let f = File::open(input_fname).unwrap();
    let reader = BufReader::new(f);
    let mut nice_strings_1 = 0;
    let mut nice_strings_2 = 0;
    for line in reader.lines() {
        let l = &(line.unwrap()[..]);
        if passes_rule_1(l) {
            nice_strings_1 += 1;
        }
        if passes_rule_2(l) {
            println!("Good rule 2: {}", l);
            nice_strings_2 += 1;
        }
    }
    println!("Nice strings 1: {}", nice_strings_1);
    println!("Nice strings 2: {}", nice_strings_2);
}