From b705b68051c262a5448251a826ffd6147cece64c Mon Sep 17 00:00:00 2001
From: David Ashby <delta.mu.alpha@gmail.com>
Date: Mon, 26 Dec 2022 14:36:04 -0700
Subject: [PATCH] finally finish day 9 part 2

---
 09/main.go | 179 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 179 insertions(+)
 create mode 100644 09/main.go

diff --git a/09/main.go b/09/main.go
new file mode 100644
index 0000000..4f8b05b
--- /dev/null
+++ b/09/main.go
@@ -0,0 +1,179 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+	"time"
+)
+
+func mustAtoi(line string) int {
+	i, _ := strconv.Atoi(line)
+	return i
+}
+
+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)
+}
+
+func makeScanner(test bool) *bufio.Scanner {
+	var f *os.File
+	if test {
+		f, _ = os.Open("inputs/testinput")
+	} else {
+		f, _ = os.Open("inputs/input")
+	}
+	reader := bufio.NewReader(f)
+	return bufio.NewScanner(reader)
+}
+
+type coord struct {
+	x int
+	y int
+}
+
+func moveNextKnot(parent, child *coord) {
+	if parent.y-child.y == 2 {
+		child.y++
+		if parent.x-child.x == 2 {
+			child.x++
+		} else if child.x-parent.x == 2 {
+			child.x--
+		} else {
+			child.x = parent.x
+		}
+	}
+	if child.y-parent.y == 2 {
+		child.y--
+		if parent.x-child.x == 2 {
+			child.x++
+		} else if child.x-parent.x == 2 {
+			child.x--
+		} else {
+			child.x = parent.x
+		}
+	}
+	if parent.x-child.x == 2 {
+		child.x++
+		if parent.y-child.y == 2 {
+			child.y++
+		} else if child.y-parent.y == 2 {
+			child.y--
+		} else {
+			child.y = parent.y
+		}
+	}
+	if child.x-parent.x == 2 {
+		child.x--
+		if parent.y-child.y == 2 {
+			child.y++
+		} else if child.y-parent.y == 2 {
+			child.y--
+		} else {
+			child.y = parent.y
+		}
+	}
+}
+
+func displayGrid(rope []coord) {
+	for x := 0; x < 10; x++ {
+		for y := 0; y < 10; y++ {
+			printed := false
+			for k, c := range rope {
+				if c.x == x && c.y == y && !printed {
+					printed = true
+					if k == 0 {
+						fmt.Print("H")
+					} else {
+						fmt.Print(k)
+					}
+				}
+			}
+			if !printed {
+				fmt.Print(".")
+			}
+		}
+		fmt.Println()
+	}
+}
+
+func partOne() {
+	scanner := makeScanner(false)
+
+	grid := map[coord]bool{{x: 0, y: 0}: true}
+	head := coord{x: 0, y: 0}
+	tail := coord{x: 0, y: 0}
+
+	for scanner.Scan() {
+		line := scanner.Text()
+		l := strings.Split(line, " ")
+		direction, steps := l[0], mustAtoi(l[1])
+		for i := 0; i < steps; i++ {
+			switch direction {
+			case "U":
+				head.y++
+			case "D":
+				head.y--
+			case "L":
+				head.x--
+			case "R":
+				head.x++
+			default:
+				panic("oh no")
+			}
+			moveNextKnot(&head, &tail)
+			grid[tail] = true
+		}
+	}
+	fmt.Println(len(grid))
+}
+
+func partTwo() {
+	scanner := makeScanner(false)
+
+	grid := map[coord]bool{{x: 0, y: 0}: true}
+	rope := []coord{
+		{x: 0, y: 0},
+		{x: 0, y: 0},
+		{x: 0, y: 0},
+		{x: 0, y: 0},
+		{x: 0, y: 0},
+		{x: 0, y: 0},
+		{x: 0, y: 0},
+		{x: 0, y: 0},
+		{x: 0, y: 0},
+		{x: 0, y: 0},
+	}
+
+	for scanner.Scan() {
+		line := scanner.Text()
+		l := strings.Split(line, " ")
+		direction, steps := l[0], mustAtoi(l[1])
+		for i := 0; i < steps; i++ {
+			switch direction {
+			case "U":
+				rope[0].y++
+			case "D":
+				rope[0].y--
+			case "L":
+				rope[0].x--
+			case "R":
+				rope[0].x++
+			default:
+				panic("oh no")
+			}
+			for i := 0; i < 9; i++ {
+				moveNextKnot(&rope[i], &rope[i+1])
+			}
+			grid[rope[9]] = true
+		}
+	}
+	fmt.Println(len(grid))
+}