Day 05

diff --git a/src/day02.rs b/src/day02.rs
index 1b88e99..60c558b 100644 (file)
--- a/src/day02.rs
+++ b/src/day02.rs
@@ -2,6 +2,8 @@ use std::io::BufRead;
 
 use itertools::{self, Itertools};
 
+use crate::utils;
+
 type Reports = Vec<Vec<i32>>;
 
 pub fn read_reports<R>(reader: R) -> Reports
@@ -10,12 +12,7 @@ where
 {
     let mut reports = Vec::<Vec<i32>>::new();
     for l in reader.lines() {
-        reports.push(
-            l.unwrap()
-                .split(' ')
-                .map(|level| level.parse::<i32>().unwrap())
-                .collect(),
-        );
+        reports.push(utils::split_to_vec(&l.unwrap(), " "));
     }
     reports
 }

diff --git a/src/day05.rs b/src/day05.rs
new file mode 100644 (file)
index 0000000..983ceff
--- /dev/null
+++ b/src/day05.rs
@@ -0,0 +1,149 @@
+use std::{io::BufRead, mem::swap};
+
+use itertools::{self, Itertools};
+
+use crate::utils;
+
+#[derive(Debug)]
+pub struct PageOrdering {
+    ordering: [Vec<i32>; 100],
+}
+
+impl PageOrdering {
+    pub fn new() -> PageOrdering {
+        PageOrdering {
+            ordering: [const { vec![] }; 100],
+        }
+    }
+
+    pub fn add_page_order(&mut self, p1: i32, p2: i32) {
+        let following_page = self.ordering.get_mut(p1 as usize).unwrap();
+        if !following_page.contains(&p2) {
+            following_page.push(p2);
+        }
+    }
+
+    pub fn get_followin_page(&self, p: i32) -> &[i32] {
+        &self.ordering[p as usize]
+    }
+}
+
+type Updates = Vec<Vec<i32>>;
+
+pub fn read_ordering_and_updates<R>(reader: R) -> (PageOrdering, Updates)
+where
+    R: BufRead,
+{
+    let lines = reader.lines().map(Result::unwrap).collect::<Vec<String>>();
+    let mut lines_iter = lines.iter();
+
+    let mut page_ordering = PageOrdering::new();
+    while let Some(l) = lines_iter.next() {
+        if l.is_empty() {
+            break;
+        }
+        let pages = utils::split_to_vec(&l, "|");
+        page_ordering.add_page_order(pages[0], pages[1]);
+    }
+
+    let mut updates: Vec<Vec<i32>> = vec![];
+    while let Some(l) = lines_iter.next() {
+        updates.push(utils::split_to_vec(&l, ","));
+    }
+
+    (page_ordering, updates)
+}
+
+pub fn sum_of_mid_page_from_valid_updates(page_ordering: &PageOrdering, updates: &Updates) -> i32 {
+    let mut sum = 0;
+    'next_update: for update in updates {
+        for (p1, p2) in update.iter().tuple_windows() {
+            if !page_ordering.get_followin_page(*p1).contains(p2) {
+                continue 'next_update;
+            }
+        }
+        sum += update[update.len() / 2];
+    }
+
+    sum
+}
+
+pub fn sum_of_mid_page_from_corrected_updates(
+    page_ordering: &PageOrdering,
+    updates: &Updates,
+) -> i32 {
+    let mut sum = 0;
+    for update in updates {
+        let l = update.len();
+        let mut updates_corrected = update.clone();
+        let mut modified = false;
+        let mut i = 0;
+        while i < l - 1 {
+            if !page_ordering
+                .get_followin_page(updates_corrected[i])
+                .contains(&updates_corrected[i + 1])
+            {
+                updates_corrected.swap(i, i + 1);
+                modified = true;
+                if i > 0 {
+                    i -= 1;
+                }
+            } else {
+                i += 1;
+            }
+        }
+        if modified {
+            sum += updates_corrected[update.len() / 2];
+        }
+    }
+
+    sum
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    static PAGE_ORDERING_AND_UPDATES: &str = "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 test_part1() {
+        let (ordering, updates) = read_ordering_and_updates(PAGE_ORDERING_AND_UPDATES.as_bytes());
+        let s = sum_of_mid_page_from_valid_updates(&ordering, &updates);
+        assert_eq!(s, 143);
+    }
+
+    #[test]
+    fn test_part2() {
+        let (ordering, updates) = read_ordering_and_updates(PAGE_ORDERING_AND_UPDATES.as_bytes());
+        let s = sum_of_mid_page_from_corrected_updates(&ordering, &updates);
+        assert_eq!(s, 123);
+    }
+}

diff --git a/src/days.rs b/src/days.rs
index 5450666..2bc4038 100644 (file)
--- a/src/days.rs
+++ b/src/days.rs
@@ -41,3 +41,13 @@ pub fn day04() -> String {
         day04::nb_of_mas_cross(&word_search)
     )
 }
+
+pub fn day05() -> String {
+    let f = fs::File::open("data/day05.input").unwrap();
+    let (ordering, updates) = day05::read_ordering_and_updates(BufReader::new(f));
+    format!(
+        "part1: {}, part2: {}",
+        day05::sum_of_mid_page_from_valid_updates(&ordering, &updates),
+        day05::sum_of_mid_page_from_corrected_updates(&ordering, &updates)
+    )
+}

diff --git a/src/main.rs b/src/main.rs
index f51a684..c15ed2e 100644 (file)
--- a/src/main.rs
+++ b/src/main.rs
@@ -7,7 +7,7 @@ mod day01;
 mod day02;
 mod day03;
 mod day04;
-// mod day05;
+mod day05;
 // mod day06;
 // mod day07;
 // mod day08;
@@ -28,6 +28,7 @@ mod day04;
 // mod day23;
 // mod day24;
 mod days;
+mod utils;
 
 #[derive(Parser, Debug)]
 #[command(author = "Greg Burri", version = "1.0", about = "Advent of Code 2024")]
@@ -47,7 +48,7 @@ fn main() {
         days::day02,
         days::day03,
         days::day04,
-        // days::day05,
+        days::day05,
         // days::day06,
         // days::day07,
         // days::day08,

diff --git a/src/utils.rs b/src/utils.rs
new file mode 100644 (file)
index 0000000..135bd36
--- /dev/null
+++ b/src/utils.rs
@@ -0,0 +1,9 @@
+use std::{fmt::Debug, str::FromStr};
+
+pub fn split_to_vec<T>(str: &str, pat: &str) -> Vec<T>
+where
+    T: FromStr,
+    <T as FromStr>::Err: Debug,
+{
+    str.split(pat).map(|v| v.parse::<T>().unwrap()).collect()
+}