feat: Day 4: Repose Record (part 2)

Author: mariotacke

day-04-repose-record/README.md

@@ -55,5 +55,13 @@ While this example listed the entries in chronological order, your entries are i
 
 **What is the ID of the guard you chose multiplied by the minute you chose?** (In the above example, the answer would be `10 * 24 = 240`.)
 
+## Part Two
+
+**Strategy 2**: Of all guards, which guard is most frequently asleep on the same minute?
+
+In the example above, Guard #**99** spent minute **45** asleep more than any other guard or minute - three times in total. (In all other cases, any guard spent any minute asleep at most twice.)
+
+**What is the ID of the guard you chose multiplied by the minute you chose?** (In the above example, the answer would be `99 * 45 = 4455`.)
+
 ## References
 - https://adventofcode.com/2018/day/4

day-04-repose-record/sleep2.js

@@ -0,0 +1,67 @@
+class Guard {
+  constructor (id) {
+    this.id = id;
+    this.minutesAsleep = Array.from({ length: 60 }).map(() => 0);
+    this.fellAsleepAt = null;
+  }
+
+  sleep (fellAsleepAt) {
+    this.fellAsleepAt = fellAsleepAt;
+  }
+
+  awake (awokeAt) {
+    for (let i = this.fellAsleepAt; i < awokeAt; i++) {
+      this.minutesAsleep[i] += 1;
+    }
+  }
+
+  get sleepiestMinute () {
+    return this.minutesAsleep
+      .map((value, index) => ({ index, value }))
+      .sort((a, b) => b.value - a.value)[0].index;
+  }
+}
+
+const sleep = (input) => {
+  const guards = {};
+  const schedule = input
+    .split('\n')
+    .map((x) => x.trim())
+    .sort()
+    .map((x) => {
+      const parts = x.match(/\[(\d{4})-(\d{2})-(\d{2}) (\d{2}):(\d{2})\] (.*)/);
+
+      return {
+        minute: +parts[5],
+        message: parts[6],
+      };
+    });
+
+  let currentGuard = null;
+
+  for (let i = 0; i < schedule.length; i++) {
+    const { message, minute } = schedule[i];
+
+    if (/Guard/.test(message)) {
+      const parts = message.match(/Guard #(\d+) begins shift/);
+      const guardId = +parts[1];
+      const guard = guards[guardId] ? guards[guardId] : new Guard(guardId);
+
+      currentGuard = guards[guardId] = guard;
+    } else if (message === 'falls asleep') {
+      currentGuard.sleep(minute);
+    } else if (message === 'wakes up') {
+      currentGuard.awake(minute);
+    }
+  }
+
+  const sleepiestGuard = Object
+    .keys(guards)
+    .map((guardId) => guards[guardId])
+    .sort((a, b) => b.minutesAsleep[b.sleepiestMinute] -
+                    a.minutesAsleep[a.sleepiestMinute])[0];
+
+  return sleepiestGuard.id * sleepiestGuard.sleepiestMinute;
+};
+
+module.exports = sleep;

day-04-repose-record/test.js

@@ -1,9 +1,10 @@
 const assert = require('assert');
 
 const sleep = require('./sleep');
+const sleep2 = require('./sleep2');
 
 describe('Day 4: Repose Record', () => {
-  it('should determine sleepiest guard', () => {
+  it('should determine sleepiest guard (strategy 1)', () => {
     const schedule =
       `[1518-11-01 00:00] Guard #10 begins shift
        [1518-11-01 00:05] falls asleep
@@ -25,4 +26,29 @@ describe('Day 4: Repose Record', () => {
 
     assert.strictEqual(sleep(schedule), 240);
   });
+
+  describe('Part Two', () => {
+    it('should determine sleepiest guard (strategy 2)', () => {
+      const schedule =
+        `[1518-11-01 00:00] Guard #10 begins shift
+         [1518-11-01 00:05] falls asleep
+         [1518-11-01 00:25] wakes up
+         [1518-11-01 00:30] falls asleep
+         [1518-11-01 00:55] wakes up
+         [1518-11-01 23:58] Guard #99 begins shift
+         [1518-11-02 00:40] falls asleep
+         [1518-11-02 00:50] wakes up
+         [1518-11-03 00:05] Guard #10 begins shift
+         [1518-11-03 00:24] falls asleep
+         [1518-11-03 00:29] wakes up
+         [1518-11-04 00:02] Guard #99 begins shift
+         [1518-11-04 00:36] falls asleep
+         [1518-11-04 00:46] wakes up
+         [1518-11-05 00:03] Guard #99 begins shift
+         [1518-11-05 00:45] falls asleep
+         [1518-11-05 00:55] wakes up`;
+
+      assert.strictEqual(sleep2(schedule), 4455);
+    });
+  });
 });