Add day 4 2018 part 2

2018/src/bin/day4.rs

@@ -3,10 +3,10 @@ extern crate lazy_static;
 extern crate chrono;
 extern crate regex;
 
-use chrono::{DateTime, TimeZone, Utc, Duration, Timelike};
+use chrono::{DateTime, Duration, TimeZone, Timelike, Utc};
 use regex::Regex;
-use std::fs;
 use std::collections::HashMap;
+use std::fs;
 
 #[derive(Debug)]
 enum Action {
@@ -21,6 +21,14 @@ struct Entry {
     action: Action,
 }
 
+impl Entry {
+    fn new(time: DateTime<Utc>, action: Action) -> Self {
+        Self { time, action }
+    }
+}
+
+// If anyone is reading this, it's not great Rust code...
+
 fn main() {
     let input = fs::read_to_string("input/day4.txt").expect("input");
 
@@ -33,25 +41,66 @@ fn main() {
         entries.sort_unstable_by(|a, b| a.time.cmp(&b.time));
         entries
     };
+    let entries_by_guard = entries_by_guard(&entries);
 
-    part1(&entries);
+    part1(&entries_by_guard);
+    part2(&entries_by_guard);
 }
 
-fn part1(entries: &[Entry]) {
+fn part1(entries_by_guard: &HashMap<u32, Vec<&Entry>>) {
-    // First group entries by guard
+    // Find the one that was asleep the most
-    let entries_by_guard = entries_by_guard(entries);
-
-    // Next find the one that was asleep the most
     let guards_by_time_asleep = calculate_time_asleep(&entries_by_guard);
-    let asleep_the_most = guards_by_time_asleep.iter().max_by(|(_guard_id, time_asleep), (_other_guard_id, other_time_asleep)| time_asleep.cmp(other_time_asleep));
+    let asleep_the_most = guards_by_time_asleep.iter().max_by(
-    println!("{:?}", asleep_the_most);
+        |(_guard_id, time_asleep), (_other_guard_id, other_time_asleep)| {
+            time_asleep.cmp(other_time_asleep)
+        },
+    );
 
     // Now find the minute that guard is asleep the most
     let sleepiest_guard = asleep_the_most.unwrap().0;
     let sleep_by_minute = sleep_by_minute(&entries_by_guard[sleepiest_guard]);
-    let sleepiest_minute = sleep_by_minute.iter().max_by(|(_minute, count), (_other_minute, other_count)| count.cmp(other_count)).unwrap();
+    let sleepiest_minute = sleep_by_minute
+        .iter()
+        .max_by(|(_minute, count), (_other_minute, other_count)| count.cmp(other_count))
+        .unwrap();
 
-    println!("Day 1: {}", sleepiest_minute.0 * sleepiest_guard);
+    println!("Part 1: {}", sleepiest_minute.0 * sleepiest_guard);
+}
+
+fn part2(entries_by_guard: &HashMap<u32, Vec<&Entry>>) {
+    let results: HashMap<_, _> = entries_by_guard
+        .keys()
+        .filter_map(|guard_id| {
+            let sleep_by_minute = sleep_by_minute(&entries_by_guard[&guard_id]);
+
+            if sleep_by_minute.is_empty() {
+                None
+            } else {
+                Some((guard_id, sleep_by_minute))
+            }
+        })
+        .collect();
+
+    // Now find the answer
+    if let Some((guard_id, minute_counts)) =
+        results
+            .iter()
+            .max_by(|(_, minute_counts), (_, other_minute_counts)| {
+                max_minute(&minute_counts)
+                    .1
+                    .cmp(&max_minute(&other_minute_counts).1)
+            })
+    {
+        let minute = max_minute(minute_counts).0;
+        println!(
+            "Part 2: guard {} * minute {} = {}",
+            *guard_id,
+            minute,
+            *guard_id * minute
+        );
+    } else {
+        println!("Part 2: No result found");
+    }
 }
 
 fn entries_by_guard(entries: &[Entry]) -> HashMap<u32, Vec<&Entry>> {
@@ -59,19 +108,25 @@ fn entries_by_guard(entries: &[Entry]) -> HashMap<u32, Vec<&Entry>> {
     let mut current_guard = None;
 
     for entry in entries {
-        println!("{:?}", entry);
-
         match entry.action {
             Action::BeginShift(guard_id) => {
-                let guard_entry = entries_by_guard.entry(guard_id).or_insert_with(|| Vec::new());
+                let guard_entry = entries_by_guard
+                    .entry(guard_id)
+                    .or_insert_with(|| Vec::new());
                 guard_entry.push(entry);
                 current_guard = Some(guard_id);
             }
             Action::FallAsleep => {
-                entries_by_guard.get_mut(&current_guard.unwrap()).unwrap().push(entry);
+                entries_by_guard
+                    .get_mut(&current_guard.unwrap())
+                    .unwrap()
+                    .push(entry);
             }
             Action::WakeUp => {
-                entries_by_guard.get_mut(&current_guard.unwrap()).unwrap().push(entry);
+                entries_by_guard
+                    .get_mut(&current_guard.unwrap())
+                    .unwrap()
+                    .push(entry);
             }
         }
     }
@@ -87,10 +142,12 @@ fn calculate_time_asleep(entries_by_guard: &HashMap<u32, Vec<&Entry>>) -> HashMa
 
         for entry in entries {
             match entry.action {
-                Action::BeginShift(guard_id) => {}
+                Action::BeginShift(_guard_id) => {}
                 Action::FallAsleep => fell_asleep = Some(entry.time),
                 Action::WakeUp => {
-                    let total_time_asleep = time_asleep.entry(guard_id).or_insert_with(|| Duration::zero());
+                    let total_time_asleep = time_asleep
+                        .entry(guard_id)
+                        .or_insert_with(|| Duration::zero());
                     *total_time_asleep = *total_time_asleep + (entry.time - fell_asleep.unwrap());
                 }
             }
@@ -106,7 +163,7 @@ fn sleep_by_minute(entries: &[&Entry]) -> HashMap<u32, u32> {
 
     for entry in entries {
         match entry.action {
-            Action::BeginShift(guard_id) => {}
+            Action::BeginShift(_guard_id) => {}
             Action::FallAsleep => fell_asleep = Some(entry.time),
             Action::WakeUp => {
                 for minute in fell_asleep.unwrap().minute()..entry.time.minute() {
@@ -141,8 +198,10 @@ fn parse_entry(line: &str) -> Option<Entry> {
     }
 }
 
-impl Entry {
+fn max_minute(hash: &HashMap<u32, u32>) -> (u32, u32) {
-    fn new(time: DateTime<Utc>, action: Action) -> Self {
+    hash
-        Self { time, action }
+        .iter()
-    }
+        .max_by(|(_, count), (_, other_count)| count.cmp(other_count))
+        .map(|(&minute, &count)| (minute, count))
+        .unwrap()
 }