day 5 part 2

src/day05.rs

@@ -0,0 +1,112 @@
+use itertools::Itertools;
+use std::{cmp::Ordering, fs::read_to_string};
+
+pub fn day_main() {
+    let input = read_to_string("input/day05.txt").unwrap();
+    let input = input.trim();
+    println!(" part1: {}", part1(input));
+    println!(" part2: {}", part2(input));
+}
+
+type RiddleResult = usize;
+
+fn part1(input: &str) -> RiddleResult {
+    let (rules, books) = parse(input);
+    books.iter().filter(|book| {
+        valid_book(book, &rules)
+    })
+    .map(|book| book[book.len() / 2].parse::<RiddleResult>().unwrap())
+    .sum()
+}
+
+fn valid_book(book: &[&str], rules: &[(&str, &str)]) -> bool {
+    for (i, a) in book.iter().enumerate() {
+        for b in book.iter().skip(i + 1) {
+            if rules.contains(&(b, a)) {
+                return false;
+            }
+        }
+    }
+    true
+}
+
+fn parse(input: &str) -> (Vec<(&str, &str)>, Vec<Vec<&str>>) {
+    let (a, b) = input.split_once("\n\n").unwrap();
+    let rules = a.lines().map(|line| line.split_once("|").unwrap()).collect_vec();
+    let books = b.lines().map(|line| line.split(",").collect_vec()).collect_vec();
+
+    (rules, books)
+}
+
+fn part2(input: &str) -> RiddleResult {
+    let (rules, books) = parse(input);
+    books.iter().filter(|book| {
+        !valid_book(book, &rules)
+    })
+    .map(|book| fix(book, &rules))
+    .map(|book| book[book.len() / 2].parse::<RiddleResult>().unwrap())
+    .sum()
+}
+
+fn  fix<'a>(book: &'a[&str], rules: &[(&str, &str)]) -> Vec<&'a str> {
+    let mut b = book.iter().copied().collect_vec();
+    b.sort_unstable_by(|a, b| {
+        if rules.contains(&(a, b)) {
+            Ordering::Less
+        } else if rules.contains(&(b, a)) {
+            Ordering::Greater
+        } else {
+            Ordering::Equal
+        }
+    });
+    b
+}
+
+#[cfg(test)]
+mod test {
+    use crate::day05::valid_book;
+
+    use super::{part1, part2};
+
+    const TEST_INPUT: &str = r"47|53
+97|13
+97|61
+97|47
+75|29
+61|13
+75|53
+29|13
+97|29
+53|29
+61|53
+97|53
+61|29
+47|13
+75|47
+97|75
+47|61
+75|61
+47|29
+75|13
+53|13
+
+75,47,61,53,29
+97,61,53,29,13
+75,29,13
+75,97,47,61,53
+61,13,29
+97,13,75,29,47
+";
+
+    #[test]
+    fn test1() {
+        assert!(valid_book(&vec!["97", "5", "13"], &vec![("97", "13")]));
+        assert!(!valid_book(&vec!["13", "5", "97"], &vec![("97", "13")]));
+        assert_eq!(part1(TEST_INPUT), 143);
+    }
+
+    #[test]
+    fn test2() {
+        assert_eq!(part2(TEST_INPUT), 123);
+    }
+}

src/lib.rs

@@ -2,3 +2,4 @@ pub mod day01;
 pub mod day02;
 pub mod day03;
 pub mod day04;
+pub mod day05;

src/main.rs

@@ -9,6 +9,7 @@ fn main() {
         (2, day02::day_main),
         (3, day03::day_main),
         (4, day04::day_main),
+        (5, day05::day_main),
     ]);
     let day: Option<u8> = args().nth(1).and_then(|a| a.parse().ok());
     let Some(day) = day else {