From 9bfc7ee2440a196770a0114d28bc2192a6faceaa Mon Sep 17 00:00:00 2001
From: Stefan Harmuth <stefan.harmuth@docomodigital.com>
Date: Fri, 19 Feb 2021 08:35:50 +0100
Subject: [PATCH] day13p1

---
 day13/day.go   | 114 +++++++++++++++++++++++++++++++++++++++++++++++++
 inputs/13      |   2 +
 inputs/13_test |   2 +
 main.go        |   3 +-
 4 files changed, 120 insertions(+), 1 deletion(-)
 create mode 100644 day13/day.go
 create mode 100644 inputs/13
 create mode 100644 inputs/13_test

diff --git a/day13/day.go b/day13/day.go
new file mode 100644
index 0000000..8256a9a
--- /dev/null
+++ b/day13/day.go
@@ -0,0 +1,114 @@
+package day13
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+	"tools"
+)
+
+const mazeHangover int = 10
+
+var favNumber, targetX, targetY int
+var fullGrid = tools.NewGridToggle()
+
+func parseInput(input []string) (favNumber, targetX, targetY int) {
+	favNumber, _ = strconv.Atoi(input[0])
+	parts := strings.Split(input[1], ",")
+	targetX, _ = strconv.Atoi(parts[0])
+	targetY, _ = strconv.Atoi(parts[1])
+
+	return favNumber, targetX, targetY
+}
+
+func buildMaze(maxX, maxY int) tools.GridToggle {
+	maze := tools.NewGridToggle()
+
+	for x := 0; x <= maxX; x++ {
+		for y := 0; y <= maxY; y++ {
+			fullGrid.Set(x, y, tools.On)
+			theNumber := int64(x*x + 3*x + 2*x*y + y + y*y + favNumber)
+			binNumber := strconv.FormatInt(theNumber, 2)
+			ones := 0
+			for _, c := range binNumber {
+				if c == '1' {
+					ones++
+				}
+			}
+			if ones%2 != 0 {
+				maze.Set(x, y, tools.On)
+			}
+		}
+	}
+
+	return maze
+}
+
+func printMaze(maze, path tools.GridToggle) {
+	for y := 0; y <= maze.MaxY; y++ {
+		for x := 0; x <= maze.MaxX; x++ {
+			if (x == targetX && y == targetY) || (x == 1 && y == 1) {
+				fmt.Print("X")
+			} else if path.State(x, y) {
+				fmt.Print("O")
+			} else if maze.State(x, y) {
+				fmt.Print("#")
+			} else {
+				fmt.Print(".")
+			}
+		}
+		fmt.Println()
+	}
+}
+
+func shortestPathToTarget(maze, visited tools.GridToggle, startX, startY int) tools.GridToggle {
+	minSteps := fullGrid.GetOnCount()
+	var newVisited tools.GridToggle
+	visited.Set(startX, startY, tools.On)
+	origVisited := visited.Copy()
+
+	if startX == targetX && startY == targetY {
+		return visited
+	}
+
+	toCheckList := []tools.Coordinate{
+		{startX - 1, startY},
+		{startX + 1, startY},
+		{startX, startY - 1},
+		{startX, startY + 1},
+	}
+
+	for _, toCheck := range toCheckList {
+		if toCheck.X < 0 || toCheck.Y < 0 || toCheck.X > maze.MaxX || toCheck.Y > maze.MaxY {
+			continue
+		}
+
+		if !maze.State(toCheck.X, toCheck.Y) && !visited.State(toCheck.X, toCheck.Y) {
+			newVisited = shortestPathToTarget(maze, origVisited.Copy(), toCheck.X, toCheck.Y)
+			if newVisited.State(targetX, targetY) && newVisited.GetOnCount() < minSteps {
+				minSteps = newVisited.GetOnCount()
+				visited = newVisited
+			}
+		}
+	}
+
+	if minSteps < fullGrid.GetOnCount() {
+		return visited
+	} else {
+		return fullGrid
+	}
+}
+
+func Part1(puzzle tools.AoCPuzzle) interface{} {
+	favNumber, targetX, targetY = parseInput(puzzle.GetInputArray())
+	maze := buildMaze(targetX+mazeHangover, targetY+mazeHangover)
+
+	path := shortestPathToTarget(maze, tools.NewGridToggle(), 1, 1)
+	printMaze(maze, path)
+
+	return path.GetOnCount() - 1
+}
+
+func Part2(puzzle tools.AoCPuzzle) interface{} {
+	return 0
+}
diff --git a/inputs/13 b/inputs/13
new file mode 100644
index 0000000..9bbb68f
--- /dev/null
+++ b/inputs/13
@@ -0,0 +1,2 @@
+1350
+31,39
\ No newline at end of file
diff --git a/inputs/13_test b/inputs/13_test
new file mode 100644
index 0000000..69d6452
--- /dev/null
+++ b/inputs/13_test
@@ -0,0 +1,2 @@
+10
+7,4
\ No newline at end of file
diff --git a/main.go b/main.go
index 69eb51d..3307921 100644
--- a/main.go
+++ b/main.go
@@ -12,6 +12,7 @@ import (
 	"aoc2016/day09"
 	"aoc2016/day10"
 	"aoc2016/day12"
+	"aoc2016/day13"
 	"flag"
 	"fmt"
 	"os"
@@ -41,7 +42,7 @@ func initDayFunctions() {
 		10: {1: day10.Part1, 2: day10.Part2},
 		//		11: {1: day11.Part1, 2: day11.Part2},
 		12: {1: day12.Part1, 2: day12.Part2},
-		//		13: {1: day13.Part1, 2: day13.Part2},
+		13: {1: day13.Part1, 2: day13.Part2},
 		//		14: {1: day14.Part1, 2: day14.Part2},
 		//		15: {1: day15.Part1, 2: day15.Part2},
 		//		16: {1: day16.Part1, 2: day16.Part2},