Day 5

src/day5.rs

@@ -0,0 +1,47 @@
+use std::{cmp::Ordering, collections::HashMap};
+
+pub fn day5() {
+    let full_input = crate::input(5);
+    let input_parts: Vec<&str> = full_input.split("\n\n").collect();
+    let order_rules: Vec<Vec<u64>> = input_parts[0]
+        .lines()
+        .filter(|line| !line.is_empty())
+        .map(|line| line.split("|").map(|x| x.parse::<u64>().unwrap()).collect())
+        .collect();
+    let page_sets: Vec<Vec<u64>> = input_parts[1]
+        .lines()
+        .filter(|line| !line.is_empty())
+        .map(|line| line.split(",").map(|x| x.parse::<u64>().unwrap()).collect())
+        .collect();
+
+    let mut order_map: HashMap<u64, Vec<u64>> = HashMap::new();
+    for rule in order_rules.iter() {
+        let entry = order_map.entry(rule[0]).or_insert(Vec::new());
+        entry.push(rule[1]);
+    }
+
+    let sort = |a: &u64, b: &u64| {
+        if order_map.get(&a).unwrap_or(&vec![]).contains(&b) {
+            Ordering::Less
+        } else if order_map.get(&b).unwrap_or(&vec![]).contains(&a) {
+            Ordering::Greater
+        } else {
+            Ordering::Equal
+        }
+    };
+    let is_sorted = |l: &Vec<u64>| {
+        l.windows(2)
+            .all(|w| (sort)(&w[0], &w[1]) != Ordering::Greater)
+    };
+
+    let (correct, mut incorrect): (Vec<Vec<u64>>, Vec<Vec<u64>>) =
+        page_sets.into_iter().partition(is_sorted);
+
+    incorrect.iter_mut().for_each(|set| set.sort_by(sort));
+
+    let sum_correct: u64 = correct.iter().map(|set| set[set.len() / 2]).sum();
+    let sum_fixed: u64 = incorrect.iter().map(|set| set[set.len() / 2]).sum();
+
+    println!("Sum of Correct Middle Pages: {}", sum_correct);
+    println!("Sum of Fixed Middle Pages: {}", sum_fixed);
+}

src/main.rs

@@ -2,9 +2,10 @@ mod day1;
 mod day2;
 mod day3;
 mod day4;
+mod day5;
 
 fn main() {
-    day4::day4();
+    day5::day5();
 }
 
 pub fn input(day: u8) -> String {