Day 5 Part 1

day_05/Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "day_05"
+version = "0.1.0"

day_05/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "day_05"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]

day_05/small_input.txt

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+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

day_05/src/main.rs

@@ -0,0 +1,87 @@
+use std::{
+    collections::{HashMap, HashSet},
+    env,
+    error::Error,
+    fs::File,
+    io::{BufReader, prelude::*},
+};
+
+fn main() -> Result<(), Box<dyn Error>> {
+    // Handle command input
+    let args: Vec<String> = env::args().collect();
+    if args.len() != 2 {
+        panic!(
+            "{} must be run with a single argument of files name!",
+            &args[0]
+        )
+    }
+    let input_file_string = &args[1];
+
+    let buffer = BufReader::new(File::open(input_file_string)?);
+
+    let mut rules_stage = true;
+    let mut page_rules: HashMap<i64, HashSet<i64>> = HashMap::new();
+    let mut valid_page_updates: Vec<Vec<i64>> = Vec::new();
+    // Load rules that look like 1|1
+    for line in buffer.lines() {
+        let line = line?;
+        if rules_stage {
+            // Stage 1: load rules
+            if line.is_empty() {
+                // Blank line means end of rules
+                rules_stage = false;
+                println!("Page Rules: {:?}", page_rules);
+                continue;
+            }
+            let split_line: Vec<&str> = line.split("|").collect();
+            if split_line.len() != 2 {
+                Err(format!("Invalid input in rules: {}", line))?;
+            }
+
+            // parse rule line and insert into out rule sets
+            let key = split_line[0].parse::<i64>()?;
+            let value = split_line[1].parse::<i64>()?;
+            match page_rules.get_mut(&key) {
+                Some(rule) => {
+                    rule.insert(value);
+                }
+                None => {
+                    let mut new_rule_set = HashSet::new();
+                    new_rule_set.insert(value);
+                    page_rules.insert(key, new_rule_set);
+                }
+            }
+        } else {
+            // Stage 2: check updates
+            let update_page_nums: Vec<i64> = line
+                .split(",")
+                .map(|v| v.parse::<_>())
+                .collect::<Result<_, _>>()?;
+
+            let mut prev_pages: HashSet<i64> = HashSet::new();
+            let mut is_valid = true;
+            for page_num in update_page_nums.iter() {
+                if let Some(rule_set) = page_rules.get(page_num) {
+                    if !prev_pages.is_disjoint(rule_set) {
+                        is_valid = false;
+                        break;
+                    }
+                    prev_pages.insert(*page_num);
+                }
+            }
+            if is_valid {
+                valid_page_updates.push(update_page_nums);
+            }
+        }
+    }
+
+    let mut accumulator = 0;
+    for update in valid_page_updates {
+        let middle_page = update[update.len() / 2];
+        accumulator += middle_page;
+    }
+
+    println!("Sum of middle pages from valid updates: {}", accumulator);
+
+    Ok(())
+}