From 66ae46843558a1a99c9b02052755cee3c57a1c09 Mon Sep 17 00:00:00 2001
From: Anna Wiggins <annabunches@gmail.com>
Date: Tue, 4 Dec 2018 03:23:19 -0500
Subject: [PATCH] Add day 4 solution, part 1.

---
 2018/day04-1.go | 140 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 140 insertions(+)
 create mode 100644 2018/day04-1.go

diff --git a/2018/day04-1.go b/2018/day04-1.go
new file mode 100644
index 0000000..5c01886
--- /dev/null
+++ b/2018/day04-1.go
@@ -0,0 +1,140 @@
+package main
+
+import (
+	"fmt"
+	"sort"
+	"strconv"
+	"strings"
+	"time"
+
+	"internal/util"
+)
+
+func main() {
+	data := util.ReadInput()
+	shifts := ParseInput(data)
+	guards := BuildGuards(shifts)
+
+	sleepiest, sleepiestMinute := FindSleepiestData(guards)
+
+	fmt.Printf("Sleepiest Guard: %d\n", sleepiest.id)
+	fmt.Printf("Sleepiest Minute: %d\n", sleepiestMinute)
+	fmt.Printf("Result: %d\n", sleepiest.id*sleepiestMinute)
+}
+
+func FindSleepiestData(guards map[int]*Guard) (*Guard, int) {
+	var sleepiest *Guard
+	for _, guard := range guards {
+		if sleepiest == nil {
+			sleepiest = guard
+			continue
+		}
+
+		if guard.sleepTotal > sleepiest.sleepTotal {
+			sleepiest = guard
+		}
+	}
+
+	sleepiestMinute := -1
+	sleepiestCount := 0
+	for minute, sleepiness := range sleepiest.sleep {
+		if sleepiness > sleepiestCount {
+			sleepiestCount = sleepiness
+			sleepiestMinute = minute
+		}
+	}
+
+	return sleepiest, sleepiestMinute
+}
+
+type Guard struct {
+	id         int
+	sleep      [60]int
+	sleepTotal int
+}
+
+type SleepEvent struct {
+	start, end int
+}
+
+type Shift struct {
+	start       time.Time
+	guard       int
+	sleepEvents []*SleepEvent
+}
+
+// ParseInput takes the input data and creates a series of "Shift" objects,
+// which are just a structured form of the data.
+func ParseInput(rawData []string) []*Shift {
+	sort.Strings(rawData)
+
+	shifts := []*Shift{}
+	var currentShift *Shift
+	var currentSleepEvent *SleepEvent
+
+	for _, line := range rawData {
+		data := strings.Split(line, "]")
+		timestamp, _ := time.Parse("2006-01-02 15:04", data[0][1:])
+		event := data[1][1:]
+
+		// handle beginning of shift
+		if strings.HasPrefix(event, "Guard #") {
+			// save old shift first
+			if currentShift != nil {
+				shifts = append(shifts, currentShift)
+			}
+
+			// now extract the guard ID and create a new Shift object
+			guardID, _ := strconv.Atoi(strings.Split(event, " ")[1][1:])
+			currentShift = &Shift{
+				guard: guardID,
+				start: timestamp,
+			}
+		}
+
+		if strings.HasPrefix(event, "falls") {
+			currentSleepEvent = &SleepEvent{
+				start: timestamp.Minute(),
+			}
+		}
+
+		if strings.HasPrefix(event, "wakes") {
+			currentSleepEvent.end = timestamp.Minute()
+			currentShift.sleepEvents = append(currentShift.sleepEvents, currentSleepEvent)
+		}
+	}
+
+	// save last shift
+	shifts = append(shifts, currentShift)
+
+	return shifts
+}
+
+// BuildGuards takes the shift data created by ParseInput and builds a map of
+// 'guards', with a per-minute counter (and handy sum) of their sleep habits.
+func BuildGuards(data []*Shift) map[int]*Guard {
+	guards := make(map[int]*Guard)
+
+	for _, shift := range data {
+		// fetch the guard for this shift, initialize if necessary
+		var guard *Guard
+		// declaring 'ok' here seems to be the only way to keep 'guard' from becoming
+		// a local variable inside the conditional. This seems like a flaw.
+		var ok bool
+		if guard, ok = guards[shift.guard]; !ok {
+			guard = &Guard{
+				id: shift.guard,
+			}
+			guards[guard.id] = guard
+		}
+
+		for _, event := range shift.sleepEvents {
+			guard.sleepTotal += event.end - event.start
+			for i := event.start; i < event.end; i++ {
+				guard.sleep[i]++
+			}
+		}
+	}
+
+	return guards
+}