Implementation for 4a

aoc2018.go

@@ -5,6 +5,8 @@ import (
 	"os"
 	"time"
 
+	"github.com/nlowe/aoc2018/day4"
+
 	"github.com/nlowe/aoc2018/day3"
 
 	"github.com/spf13/cobra"
@@ -40,6 +42,7 @@ func main() {
 		day1.A, day1.B,
 		day2.A, day2.B,
 		day3.A, day3.B,
+		day4.A,
 	)
 
 	flags := rootCmd.PersistentFlags()

day4/a.go

@@ -0,0 +1,124 @@
+package day4
+
+import (
+	"fmt"
+	"sort"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/nlowe/aoc2018/util"
+	"github.com/spf13/cobra"
+)
+
+var A = &cobra.Command{
+	Use:   "4a",
+	Short: "Day 4, Problem A",
+	Run: func(_ *cobra.Command, _ []string) {
+		fmt.Printf("Answer: %d\n", a(util.ReadInput()))
+	},
+}
+
+const (
+	timestampLayout  = "2006-01-02 15:04"
+	ActionBeginShift = "begins shift"
+	ActionFallAsleep = "falls asleep"
+	ActionWakeUp     = "wakes up"
+)
+
+type event struct {
+	who  int
+	what string
+	when time.Time
+}
+
+func ParseEvent(line string) *event {
+	result := &event{who: -1}
+	rawTime, rest := line[1:(1+len(timestampLayout))], strings.TrimSpace(line[(2+len(timestampLayout)):])
+
+	if t, err := time.Parse(timestampLayout, rawTime); err != nil {
+		panic(err)
+	} else {
+		result.when = t
+	}
+
+	if rest == ActionFallAsleep || rest == ActionWakeUp {
+		result.what = rest
+	} else {
+		result.what = ActionBeginShift
+
+		idSlug := strings.Split(rest[7:], " ")[0]
+		if id, err := strconv.Atoi(idSlug); err != nil {
+			panic(err)
+		} else {
+			result.who = id
+		}
+	}
+
+	return result
+}
+
+type sleepNumber struct {
+	total   int
+	minutes [60]int
+}
+
+func a(input *util.ChallengeInput) int {
+	var events []*event
+
+	for line := range input.Lines() {
+		events = append(events, ParseEvent(line))
+	}
+
+	sort.Slice(events, func(i, j int) bool {
+		return events[i].when.Before(events[j].when)
+	})
+
+	patterns := map[int]*sleepNumber{}
+
+	lastGuard := 0
+	sleepingAt := 0
+	for _, event := range events {
+		if event.what == ActionBeginShift {
+			lastGuard = event.who
+		} else {
+			var tracker *sleepNumber
+			var found bool
+
+			if tracker, found = patterns[lastGuard]; !found {
+				tracker = &sleepNumber{total: 1, minutes: [60]int{}}
+				patterns[lastGuard] = tracker
+			}
+
+			if event.what == ActionFallAsleep {
+				sleepingAt = event.when.Minute()
+			} else {
+				for m := sleepingAt; m < event.when.Minute(); m++ {
+					tracker.total++
+					tracker.minutes[m]++
+				}
+			}
+		}
+	}
+
+	var candidateId int
+	var candidate *sleepNumber
+
+	for k, v := range patterns {
+		if candidate == nil || v.total > candidate.total {
+			candidateId = k
+			candidate = v
+		}
+	}
+
+	possibleMinute := 0
+	possibleResult := candidate.minutes[0]
+	for m, betterResult := range candidate.minutes[1:] {
+		if betterResult > possibleResult {
+			possibleMinute = m + 1
+			possibleResult = betterResult
+		}
+	}
+
+	return candidateId * possibleMinute
+}

day4/a_test.go

@@ -0,0 +1,30 @@
+package day4
+
+import (
+	"testing"
+
+	"github.com/nlowe/aoc2018/util"
+	"github.com/stretchr/testify/require"
+)
+
+func TestA(t *testing.T) {
+	input := util.TestInput(`[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`)
+
+	require.Equal(t, 240, a(input))
+}