From f5ec48772e2bc4977fe04bedcf917ee2e4ae0a2e Mon Sep 17 00:00:00 2001
From: David Ashby <delta.mu.alpha@gmail.com>
Date: Sat, 12 Dec 2020 12:22:14 -0500
Subject: [PATCH] add day 12

---
 .gitignore |   3 +-
 12/main.go | 198 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 200 insertions(+), 1 deletion(-)
 create mode 100644 12/main.go

diff --git a/.gitignore b/.gitignore
index 770eab4..8178bd2 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
-input
\ No newline at end of file
+input
+testinput
\ No newline at end of file
diff --git a/12/main.go b/12/main.go
new file mode 100644
index 0000000..43cf118
--- /dev/null
+++ b/12/main.go
@@ -0,0 +1,198 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"time"
+)
+
+func main() {
+	start := time.Now()
+	partOne()
+	duration := time.Since(start)
+	partTwo()
+	duration2 := time.Since(start)
+	fmt.Printf("p1: %s, p2: %s\n", duration, duration2-duration)
+}
+
+type ship struct {
+	horizontal int
+	vertical   int
+	direction  rune // E W N S
+}
+
+// both horizontal/vertical are relative to ship
+type waypoint struct {
+	horizontal int
+	vertical   int
+}
+
+func parseLine(s string) (rune, int) {
+	i, _ := strconv.Atoi(s[1:])
+	return []rune(s)[0], i
+}
+
+func movePartOne(s ship, action rune, vector int) ship {
+	switch action {
+	case 'R', 'L':
+		s.direction = rotateShip(s.direction, vector, action)
+	case 'N':
+		s.vertical = s.vertical + vector
+	case 'S':
+		s.vertical = s.vertical - vector
+	case 'E':
+		s.horizontal = s.horizontal + vector
+	case 'W':
+		s.horizontal = s.horizontal - vector
+	case 'F':
+		s = movePartOne(s, s.direction, vector)
+	}
+	return s
+}
+
+func movePartTwo(s ship, w waypoint, action rune, vector int) (ship, waypoint) {
+	switch action {
+	case 'R', 'L':
+		w = rotateWaypoint(w, action, vector)
+	case 'N':
+		w.vertical = w.vertical + vector
+	case 'S':
+		w.vertical = w.vertical - vector
+	case 'E':
+		w.horizontal = w.horizontal + vector
+	case 'W':
+		w.horizontal = w.horizontal - vector
+	case 'F':
+		s.horizontal = s.horizontal + (w.horizontal * vector)
+		s.vertical = s.vertical + (w.vertical * vector)
+	}
+	return s, w
+}
+
+// for example E, 90, L => N; E, 180, R => W; E, 90, R => S
+func rotateShip(current rune, degrees int, rl rune) rune {
+	// easy
+	if degrees == 180 {
+		switch current {
+		case 'N':
+			return 'S'
+		case 'S':
+			return 'N'
+		case 'E':
+			return 'W'
+		case 'W':
+			return 'E'
+		}
+	}
+	// translate L to R
+	if rl == 'L' {
+		if degrees == 90 {
+			degrees = 270
+		} else {
+			degrees = 90
+		}
+	}
+	// the R set
+	if degrees == 90 {
+		switch current {
+		case 'N':
+			return 'E'
+		case 'S':
+			return 'W'
+		case 'E':
+			return 'S'
+		case 'W':
+			return 'N'
+		}
+	} else if degrees == 270 {
+		switch current {
+		case 'N':
+			return 'W'
+		case 'S':
+			return 'E'
+		case 'E':
+			return 'N'
+		case 'W':
+			return 'S'
+		}
+	}
+
+	return current // we're made a terrible mistake somewhere
+}
+
+func rotateWaypoint(w waypoint, action rune, vector int) waypoint {
+	if vector == 180 {
+		w.horizontal = -w.horizontal
+		w.vertical = -w.vertical
+	} else if action == 'R' {
+		if vector == 90 {
+			w.horizontal, w.vertical = w.vertical, -w.horizontal
+		}
+		if vector == 270 {
+			w.horizontal, w.vertical = -w.vertical, w.horizontal
+		}
+	} else if action == 'L' {
+		if vector == 90 {
+			w.horizontal, w.vertical = -w.vertical, w.horizontal
+		}
+		if vector == 270 {
+			w.horizontal, w.vertical = w.vertical, -w.horizontal
+		}
+	}
+	return w
+}
+
+func manhattan(i, j int) int {
+	return abs(i) + abs(j)
+}
+
+func abs(x int) int {
+	if x < 0 {
+		return -x
+	}
+	return x
+}
+
+func partOne() {
+	f, _ := os.Open("input")
+	reader := bufio.NewReader(f)
+	scanner := bufio.NewScanner(reader)
+
+	s := ship{
+		horizontal: 0,
+		vertical:   0,
+		direction:  'E',
+	}
+
+	for scanner.Scan() {
+		dir, vec := parseLine(scanner.Text())
+		s = movePartOne(s, dir, vec)
+	}
+
+	fmt.Println(manhattan(s.horizontal, s.vertical))
+}
+
+func partTwo() {
+	f, _ := os.Open("input")
+	reader := bufio.NewReader(f)
+	scanner := bufio.NewScanner(reader)
+
+	s := ship{
+		horizontal: 0,
+		vertical:   0,
+		// no longer care about ship direction
+	}
+	w := waypoint{
+		horizontal: 10,
+		vertical:   1,
+	}
+
+	for scanner.Scan() {
+		dir, vec := parseLine(scanner.Text())
+		s, w = movePartTwo(s, w, dir, vec)
+	}
+
+	fmt.Println(manhattan(s.horizontal, s.vertical))
+}