Day 12 solution.

2020/day12.go

@@ -0,0 +1,148 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"strconv"
+
+	"git.annabunch.es/annabunches/adventofcode/2020/lib/fileutils"
+)
+
+func distance(x1, y1, x2, y2 int) int {
+	dy := y2 - y1
+	dx := x2 - x1
+	if dy < 0 {
+		dy *= -1
+	}
+	if dx < 0 {
+		dx *= -1
+	}
+	return dx + dy
+}
+
+func rotate(x, y int, direction byte, degrees int) (int, int) {
+	turns := degrees / 90
+
+	newX := x
+	newY := y
+
+	for i := 0; i < turns; i++ {
+		hold := newX
+		newX = newY
+		newY = hold
+
+		switch direction {
+		case 'L':
+			newX *= -1
+		case 'R':
+			newY *= -1
+		}
+	}
+
+	return newX, newY
+}
+
+func step1(values []string) (int, int) {
+	facing := 90
+	x := 0
+	y := 0
+
+	for _, line := range values {
+		direction := line[0]
+		value, err := strconv.Atoi(line[1:])
+		if err != nil {
+			log.Panicf(err.Error())
+		}
+		switch direction {
+		case 'N':
+			y += value
+		case 'S':
+			y -= value
+		case 'E':
+			x += value
+		case 'W':
+			x -= value
+		case 'L':
+			facing -= value
+		case 'R':
+			facing += value
+		case 'F':
+			// the hard one
+			switch facing {
+			case 0:
+				y += value
+			case 90:
+				x += value
+			case 180:
+				y -= value
+			case 270:
+				x -= value
+			default:
+				log.Panicf("Oh no, ships can't face %d degrees!", facing)
+			}
+		}
+
+		if facing < 0 {
+			facing += 360
+		}
+
+		if facing >= 360 {
+			facing %= 360
+		}
+	}
+
+	return x, y
+}
+
+func step2(values []string) (int, int) {
+	x := 0
+	y := 0
+	wayX := 10
+	wayY := 1
+
+	for _, line := range values {
+		direction := line[0]
+		value, err := strconv.Atoi(line[1:])
+		if err != nil {
+			log.Panicf(err.Error())
+		}
+		switch direction {
+		case 'N':
+			wayY += value
+		case 'S':
+			wayY -= value
+		case 'E':
+			wayX += value
+		case 'W':
+			wayX -= value
+		case 'L':
+			wayX, wayY = rotate(wayX, wayY, direction, value)
+		case 'R':
+			wayX, wayY = rotate(wayX, wayY, direction, value)
+		case 'F':
+			for i := 0; i < value; i++ {
+				x += wayX
+				y += wayY
+			}
+		}
+	}
+
+	return x, y
+}
+
+func main() {
+	step := os.Args[1]
+	values := fileutils.InputParserStrings(os.Args[2])
+
+	x := 0
+	y := 0
+	switch step {
+	case "1":
+		x, y = step1(values)
+	case "2":
+		x, y = step2(values)
+	}
+
+	fmt.Println(distance(x, y, 0, 0))
+}

2020/lib/fileutils/fileutils.go

@@ -57,7 +57,8 @@ func InputParserStrings(filename string) []string {
 	if err != nil {
 		log.Panicf(err.Error())
 	}
-	return strings.Split(string(data), "\n")
+	output := strings.Split(string(data), "\n")
+	return output[:len(output)-1]
 }
 
 func InputParserBytes(filename string) [][]byte {