From 859ac1635e828ba51130ddf549a654aa61f44a57 Mon Sep 17 00:00:00 2001
From: Ben Charlton <ben@spod.cx>
Date: Tue, 19 Dec 2017 10:23:02 +0000
Subject: [PATCH] day 19

---
 19/19.go | 98 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 98 insertions(+)
 create mode 100644 19/19.go

diff --git a/19/19.go b/19/19.go
new file mode 100644
index 0000000..7e693be
--- /dev/null
+++ b/19/19.go
@@ -0,0 +1,98 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+)
+
+// Coords are y,x as first grid array index = y coord.
+var lookpos = [][]int{{0, 1}, {1, 0}, {-1, 0}, {0, -1}}
+
+// cat input | go run 19.go
+
+func main() {
+
+	var grid []string
+
+	scanner := bufio.NewScanner(os.Stdin)
+
+	for scanner.Scan() {
+		grid = append(grid, scanner.Text())
+
+	}
+
+	cx, cy := findStart(grid)
+	dx, dy := 0, 1
+
+	steps := 0
+	for cx != -1 && cy != -1 {
+
+		switch grid[cy][cx] {
+		case '|':
+		case '-':
+		case '+':
+		default:
+			fmt.Print(string(grid[cy][cx]))
+		}
+
+		cx, cy, dx, dy = findNext(grid, cx, cy, dx, dy)
+		steps++
+	}
+	fmt.Println(steps - 1)
+
+}
+
+func findStart(grid []string) (int, int) {
+	for x := range grid[0] {
+		if grid[0][x] != ' ' {
+			return x, 0
+		}
+	}
+	return -1, -1
+}
+
+func findNext(grid []string, cx int, cy int, dx int, dy int) (int, int, int, int) {
+
+	nextX := cx + dx
+	nextY := cy + dy
+	prevX := cx - dx
+	prevY := cy - dy
+
+	current := grid[cy][cx]
+
+	if current == '+' {
+		// Check for direction change
+		for check := range lookpos {
+			xp := cx + lookpos[check][1]
+			yp := cy + lookpos[check][0]
+			//fmt.Println("pos:", xp, yp)
+
+			// Don't go backwards
+			if xp == prevX && yp == prevY {
+				continue
+			}
+			// Bounds checking
+			if xp < 0 || xp >= len(grid[0]) {
+				continue
+			}
+			if yp < 0 || yp >= len(grid) {
+				continue
+			}
+
+			// Skip blanks.
+			if grid[yp][xp] == ' ' {
+				continue
+			}
+			// Set new direction
+			dx = xp - cx
+			dy = yp - cy
+			//fmt.Println("dir:", dx, dy)
+			return xp, yp, dx, dy
+		}
+	}
+
+	// No direction change
+	return nextX, nextY, dx, dy
+
+}