[2020-12-13] Add solutions for day13.01

Makefile

@@ -39,6 +39,8 @@ day12:
 	go run main.go day12 input
 
 day13:
+	go run main.go day13 input
+
 day14:
 day15:
 day16:

day13/example.txt

@@ -0,0 +1,2 @@
+939
+7,13,x,x,59,x,31,19

day13/input.txt

@@ -0,0 +1,2 @@
+1002461
+29,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,41,x,x,x,x,x,x,x,x,x,521,x,x,x,x,x,x,x,23,x,x,x,x,13,x,x,x,17,x,x,x,x,x,x,x,x,x,x,x,x,x,601,x,x,x,x,x,37,x,x,x,x,x,x,x,x,x,x,x,x,19

day13/parse.go

@@ -0,0 +1,34 @@
+package day13
+
+import (
+	"strconv"
+	"strings"
+
+	"git.elis.nu/etu/aoc2020/utils"
+)
+
+var schedule struct {
+	Departure int
+	Lines     []int
+}
+
+func ParseFile(input string) {
+	// Parse file
+	rows := utils.GetLinesFromFile("day13/" + input + ".txt")
+
+	// Convert time
+	time, _ := strconv.Atoi(rows[0])
+
+	// Store time
+	schedule.Departure = time
+
+	for _, row := range strings.Split(rows[1], ",") {
+		if row != "x" {
+			// Convert bus number
+			line, _ := strconv.Atoi(row)
+
+			// Add to schedule
+			schedule.Lines = append(schedule.Lines, line)
+		}
+	}
+}

day13/solve1.go

@@ -0,0 +1,28 @@
+package day13
+
+import (
+	"log"
+)
+
+func Solve1() {
+	// Big number to esaier spot smaller numbers
+	lowestNextDeparture := schedule.Departure * 1000
+	lowestNextDepartureLine := 0
+
+	// Look for next departure times for lines
+	for _, line := range schedule.Lines {
+		// Calculate next departure
+		nextDeparture := schedule.Departure/line*line + line
+
+		// Look for lowest departure time
+		if nextDeparture < lowestNextDeparture {
+			lowestNextDeparture = nextDeparture
+			lowestNextDepartureLine = line
+		}
+	}
+
+	// Calculate next departure id
+	nextDepartureId := (lowestNextDeparture - schedule.Departure) * lowestNextDepartureLine
+
+	log.Printf("2020-12-13.01: Answer: %d\n", nextDepartureId)
+}

day13/solve2.go

@@ -0,0 +1,12 @@
+package day13
+
+import (
+	"fmt"
+	"log"
+)
+
+func Solve2() {
+	fmt.Println(len(schedule.Lines))
+
+	log.Printf("2020-12-13.02: Answer: %d\n", len(schedule.Lines))
+}

main.go

@@ -16,6 +16,7 @@ import (
 	"git.elis.nu/etu/aoc2020/day10"
 	"git.elis.nu/etu/aoc2020/day11"
 	"git.elis.nu/etu/aoc2020/day12"
+	"git.elis.nu/etu/aoc2020/day13"
 	"git.elis.nu/etu/aoc2020/utils"
 )
 
@@ -60,5 +61,8 @@ func main() {
 
 	case "day12":
 		utils.Perf("2020-12-12", day12.ParseFile, day12.Solve1, day12.Solve2)
+
+	case "day13":
+		utils.Perf("2020-12-13", day13.ParseFile, day13.Solve1, day13.Solve2)
 	}
 }