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use std::collections::{HashMap, HashSet};
static DAY: u8 = 5;
fn main() {
let input = advent::read_file(DAY);
println!("{DAY}a: {}", PageOrdering::new(&input).right_order_middle());
println!("{DAY}b: {}", PageOrdering::new(&input).incorrect_fixed_middle());
}
struct PageOrdering {
rules: HashMap<u32,HashSet<u32>>,
updates: Vec<Vec<u32>>,
}
impl PageOrdering {
fn new(input: &str) -> PageOrdering {
let (rules_lines, updates_lines) = input.split_once("\n\n").unwrap();
let mut rules = HashMap::new();
for rule in rules_lines.split("\n") {
let (left, right) = rule.split_once("|").unwrap();
let left = left.parse::<u32>().unwrap();
let right = right.parse::<u32>().unwrap();
rules.entry(left).or_insert(HashSet::new()).insert(right);
}
let mut updates = Vec::new();
for line in updates_lines.split_terminator("\n") {
let update = line.split(",").map(|x| x.parse::<u32>().unwrap()).collect::<Vec<_>>();
updates.push(update);
}
PageOrdering { rules, updates }
}
fn wrong_position(&self, update: &[u32]) -> Option<u32> {
for (i, page1) in update.iter().enumerate() {
for page2 in update.iter().skip(i+1) {
let before2 = match self.rules.get(page2) {
Some(r) => r,
None => continue,
};
if before2.contains(page1) {
return Some(*page1);
}
}
}
None
}
fn right_order_middle(&self) -> u32 {
let mut sum = 0;
for update in &self.updates {
if self.wrong_position(update).is_none() {
sum += update[update.len()/2];
}
}
sum
}
fn fix_order(&self, update: &[u32]) -> Vec<u32> {
let mut update = update.to_vec();
let page_cmp = |page1: u32, page2: u32| -> std::cmp::Ordering {
if let Some(rules) = self.rules.get(&page1) {
if rules.contains(&page2) {
return std::cmp::Ordering::Less;
}
}
if let Some(rules) = self.rules.get(&page2) {
if rules.contains(&page1) {
return std::cmp::Ordering::Greater;
}
}
panic!("no ordering found");
};
update.sort_by(|page1, page2| page_cmp(*page1, *page2));
update
}
fn incorrect_fixed_middle(&self) -> u32 {
let mut sum = 0;
for update in &self.updates {
if self.wrong_position(update).is_some() {
let fixed = self.fix_order(update);
sum += fixed[fixed.len()/2];
}
}
sum
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test() {
let input =
"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";
assert_eq!(PageOrdering::new(input).right_order_middle(), 143);
assert_eq!(PageOrdering::new(input).incorrect_fixed_middle(), 123);
}
}
|
