From 358d1ad23d524250886c89b6122cd6bd71a2575b Mon Sep 17 00:00:00 2001
From: Nihilazo <nico@itwont.work>
Date: Sat, 12 Dec 2020 22:46:59 +0000
Subject: [PATCH] solve day 12 part 2

---
 day12/main.go | 70 ++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 56 insertions(+), 14 deletions(-)

diff --git a/day12/main.go b/day12/main.go
index 15aa3a6..f86c2b5 100644
--- a/day12/main.go
+++ b/day12/main.go
@@ -7,10 +7,16 @@ import (
 	"fmt"
 )
 
+type Instruction struct{
+	Op rune
+	Arg int
+}
 type Ship struct{
 	NS int // North-South position
 	EW int // East-West position
 	Facing int // N: 0, E: 1, S: 2, W: 3
+	WayNS int // Waypoint North-South position
+	WayEW int // Waypoint East-West position
 }
 
 // abs is a simple local abs for integers to avoid importing math
@@ -26,43 +32,79 @@ func main() {
 	ship := Ship{Facing: 1}
 	d, _ := ioutil.ReadFile("input")
 	lines := strings.Split(string(d),"\n") // I feel like I write this for EVERY AoC
+	var prog []Instruction
 	for _, l := range lines {
 		if l != "" {
 			command := l[0] // Not unicode-safe! But input is known to contain only ASCII chars
 			num, _ := strconv.Atoi(l[1:])
-			switch rune(command) {
+			prog = append(prog, Instruction{Op: rune(command), Arg: num})
+		}
+	}
+	for _, l := range prog {
+			switch l.Op {
 				case 'F':
 					switch ship.Facing {
 						case 0:
-							ship.NS += num
+							ship.NS += l.Arg
 						case 2:
-							ship.NS -= num
+							ship.NS -= l.Arg
 						case 1:							
-							ship.EW += num
+							ship.EW += l.Arg
 						case 3:							
-							ship.EW -= num
+							ship.EW -= l.Arg
 						}
 				case 'N':
-					ship.NS += num
+					ship.NS += l.Arg
 				case 'S':
-					ship.NS -= num
+					ship.NS -= l.Arg
 				case 'E':
-					ship.EW += num
+					ship.EW += l.Arg
 				case 'W':
-					ship.EW -= num
+					ship.EW -= l.Arg
 				case 'R':
-					h := num/90
+					h := l.Arg/90
 					f := ship.Facing + h
 					ship.Facing = ((f%4)+4)%4
 				case 'L':
-					h := num/90
+					h := l.Arg/90
 					f := ship.Facing - h
 					ship.Facing = ((f%4)+4)%4
 			}
-			fmt.Printf("INSTRUCTION: %s, FACING: %d, N/S POS: %d, E/W POS: %d\n",l, ship.Facing, ship.NS, ship.EW)
+	}
+	fmt.Println("Part 1:", abs(ship.EW)+abs(ship.NS))
+	// Part 2 - we use the waypoint this time
+	ship = Ship{Facing: 1, WayNS: 1, WayEW: 10}
+	for _, l := range prog {
+		switch l.Op {
+			case 'F':
+				NS := l.Arg*ship.WayNS
+				EW := l.Arg*ship.WayEW
+				ship.NS += NS
+				ship.EW += EW
+			case 'N':
+				ship.WayNS += l.Arg
+			case 'S':
+				ship.WayNS -= l.Arg
+			case 'E':
+				ship.WayEW += l.Arg
+			case 'W':
+				ship.WayEW -= l.Arg
+			case 'R':
+				for i := l.Arg; i != 0; i -= 90 {
+					NS := -ship.WayEW
+					EW := ship.WayNS
+					ship.WayEW = EW
+					ship.WayNS = NS
+				}
+			case 'L':
+				for i := l.Arg*3; i != 0; i -= 90 {
+					NS := -ship.WayEW
+					EW := ship.WayNS
+					ship.WayEW = EW
+					ship.WayNS = NS
+				}
 		}
 	}
-	fmt.Println(ship)
-	fmt.Println("Part 1:", abs(ship.EW)+abs(ship.NS))
+	fmt.Println("Part 2:", abs(ship.EW)+abs(ship.NS))
 	
 }
\ No newline at end of file