From 975bc3346d86d2e620ae3deb50255d995af1df1c Mon Sep 17 00:00:00 2001
From: alexchao26 <alexchaoo@gmail.com>
Date: Sat, 12 Dec 2020 01:14:53 -0500
Subject: [PATCH] 2020-day12: 243 on part 1, then confused the heck out of
 myself for part 2 w/ x/y vs row/col vs x,y coordinates and rotating around
 the origin..

---
 2020/day12/main.go      | 108 +++++++++++++++++++++++++++++++++++-----
 2020/day12/main_test.go |  20 ++++++--
 2 files changed, 111 insertions(+), 17 deletions(-)

diff --git a/2020/day12/main.go b/2020/day12/main.go
index eac4896..c396f7e 100644
--- a/2020/day12/main.go
+++ b/2020/day12/main.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"strings"
 
+	"github.com/alexchao26/advent-of-code-go/mathutil"
 	"github.com/alexchao26/advent-of-code-go/util"
 )
 
@@ -16,35 +17,118 @@ func main() {
 
 	if part == 1 {
 		ans := part1(util.ReadFile("./input.txt"))
-		util.CopyToClipboard(fmt.Sprintf("%v", ans))
 		fmt.Println("Output:", ans)
 	} else {
 		ans := part2(util.ReadFile("./input.txt"))
-		util.CopyToClipboard(fmt.Sprintf("%v", ans))
 		fmt.Println("Output:", ans)
 	}
 }
 
-func part1(input string) int {
-	parsed := parseInput(input)
-	_ = parsed
+// globals for part 1
+var directions = []string{"N", "E", "S", "W"}
+var directionsToDiff = map[string][2]int{
+	// !! X and Y like a coordinate system! Not typical 2D matrices in algos
+	"N": [2]int{0, 1},
+	"E": [2]int{1, 0},
+	"S": [2]int{0, -1},
+	"W": [2]int{-1, 0},
+}
 
-	return 0
+func part1(input string) int {
+	instructions := parseInput(input)
+
+	// X and Y like a coordinate system
+	var shipX, shipY int
+	dirIndex := 1 // index in directions slice
+	for _, inst := range instructions {
+		switch inst.action {
+		case "N":
+			shipY += inst.value
+		case "S":
+			shipY -= inst.value
+		case "E":
+			shipX += inst.value
+		case "W":
+			shipX -= inst.value
+		case "L":
+			// rotate ship left, this is equivalent
+			// -1 + 4 to keeping dirIndex positive for the modding
+			dirIndex += (-1 + 4) * inst.value / 90
+			dirIndex %= 4
+		case "R":
+			dirIndex += inst.value / 90
+			dirIndex %= 4
+		case "F":
+			d := directionsToDiff[directions[dirIndex]]
+			shipX += d[0] * inst.value
+			shipY += d[1] * inst.value
+		default:
+			panic("unexpected action")
+		}
+	}
+
+	return mathutil.ManhattanDistance(0, 0, shipX, shipY)
 }
 
 func part2(input string) int {
-	parsed := parseInput(input)
-	_ = parsed
+	instructions := parseInput(input)
 
-	return 0
+	// X and Y like a coordinate system
+	waypointX := 10
+	waypointY := 1
+	var shipX, shipY int
+
+	for _, inst := range instructions {
+		switch inst.action {
+		case "N":
+			waypointY += inst.value
+		case "S":
+			waypointY -= inst.value
+		case "E":
+			waypointX += inst.value
+		case "W":
+			waypointX -= inst.value
+		case "L":
+			// rotate waypoint left around ship (origin)
+			turns := inst.value / 90
+			for turns > 0 {
+				// this simple bit is all it needs to rotate around the origin
+				// I had a 20 line if/else block...
+				waypointX, waypointY = -waypointY, waypointX
+				turns--
+			}
+		case "R":
+			turns := inst.value / 90
+			for turns > 0 {
+				waypointX, waypointY = waypointY, -waypointX
+				turns--
+			}
+		case "F":
+			shipX += inst.value * waypointX
+			shipY += inst.value * waypointY
+		default:
+			panic("unexpected action")
+		}
+	}
+
+	return mathutil.ManhattanDistance(0, 0, shipX, shipY)
 }
 
-func parseInput(input string) []int {
-	var ans []int
+type instruction struct {
+	action string
+	value  int
+}
+
+func parseInput(input string) []instruction {
+	var ans []instruction
 
 	lines := strings.Split(input, "\n")
 	for _, l := range lines {
-		ans = append(ans, mathutil.StrToInt(l))
+		inst := instruction{
+			action: l[:1],
+			value:  mathutil.StrToInt(l[1:]),
+		}
+		ans = append(ans, inst)
 	}
 
 	return ans
diff --git a/2020/day12/main_test.go b/2020/day12/main_test.go
index ee82d4e..ed3fe01 100644
--- a/2020/day12/main_test.go
+++ b/2020/day12/main_test.go
@@ -1,14 +1,24 @@
 package main
 
-import "testing"
+import (
+	"testing"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+var exampleInput = `F10
+N3
+F7
+R90
+F11`
 
 var tests1 = []struct {
 	name  string
 	want  int
 	input string
-	// add extra args if needed
 }{
-	// {"actual", ACTUAL_ANSWER, util.ReadFile("input.txt")},
+	{"example", 25, exampleInput},
+	{"actual", 820, util.ReadFile("input.txt")},
 }
 
 func TestPart1(t *testing.T) {
@@ -25,9 +35,9 @@ var tests2 = []struct {
 	name  string
 	want  int
 	input string
-	// add extra args if needed
 }{
-	// {"actual", ACTUAL_ANSWER, util.ReadFile("input.txt")},
+	{"example", 286, exampleInput},
+	{"actual", 66614, util.ReadFile("input.txt")},
 }
 
 func TestPart2(t *testing.T) {