From 0dadb796bc9df1564fd54a4c619e427cc74d7532 Mon Sep 17 00:00:00 2001
From: Alphyron <admin@dragon-labs.de>
Date: Tue, 10 Dec 2019 12:33:22 +0100
Subject: [PATCH] :sparkles: Finish part 1 of day 10

---
 day10/input.txt |  28 +++++++++
 day10/main.go   | 152 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 180 insertions(+)
 create mode 100644 day10/input.txt
 create mode 100644 day10/main.go

diff --git a/day10/input.txt b/day10/input.txt
new file mode 100644
index 0000000..2dd7815
--- /dev/null
+++ b/day10/input.txt
@@ -0,0 +1,28 @@
+###..#.##.####.##..###.#.#..
+#..#..###..#.......####.....
+#.###.#.##..###.##..#.###.#.
+..#.##..##...#.#.###.##.####
+.#.##..####...####.###.##...
+##...###.#.##.##..###..#..#.
+.##..###...#....###.....##.#
+#..##...#..#.##..####.....#.
+.#..#.######.#..#..####....#
+#.##.##......#..#..####.##..
+##...#....#.#.##.#..#...##.#
+##.####.###...#.##........##
+......##.....#.###.##.#.#..#
+.###..#####.#..#...#...#.###
+..##.###..##.#.##.#.##......
+......##.#.#....#..##.#.####
+...##..#.#.#.....##.###...##
+.#.#..#.#....##..##.#..#.#..
+...#..###..##.####.#...#..##
+#.#......#.#..##..#...#.#..#
+..#.##.#......#.##...#..#.##
+#.##..#....#...#.##..#..#..#
+#..#.#.#.##..#..#.#.#...##..
+.#...#.........#..#....#.#.#
+..####.#..#..##.####.#.##.##
+.#.######......##..#.#.##.#.
+.#....####....###.#.#.#.####
+....####...##.#.#...#..#.##.
diff --git a/day10/main.go b/day10/main.go
new file mode 100644
index 0000000..555e441
--- /dev/null
+++ b/day10/main.go
@@ -0,0 +1,152 @@
+package main
+
+import (
+	"bufio"
+	"log"
+	"math"
+	"os"
+)
+
+type Position struct {
+	X int
+	Y int
+}
+
+func main() {
+	file, err := os.Open("input.txt")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer file.Close()
+
+	t2 := make([]string, 0)
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		t2 = append(t2, scanner.Text())
+	}
+
+	field, asteroids := ParseStringSliceToField(t2)
+
+	SolvePzl1(field, asteroids)
+}
+
+func SolvePzl1(field [][]int, asteroids []Position) {
+	highestFoundAstros := math.MinInt32
+	pos := Position{}
+
+	for _, astro := range asteroids {
+		sum := CountAsteroidsFromPosition(field, astro.X, astro.Y)
+		if highestFoundAstros < sum {
+			highestFoundAstros = sum
+			pos = astro
+		}
+	}
+
+	log.Printf("Part1: Found %d Astros at Position(%d,%d) from %d Astros", highestFoundAstros, pos.X, pos.Y, len(asteroids))
+}
+
+func ParseStringSliceToField(view []string) (field [][]int, asteroids []Position) {
+	field = make([][]int, 0)
+	asteroids = make([]Position, 0)
+
+	x, y := 0, 0
+
+	for i, line := range view {
+		x = 0
+		field = append(field, make([]int, 0))
+		for j := 0; j < len(line); j++ {
+			if "#" == string(line[j]) {
+				field[i] = append(field[i], 0)
+				asteroids = append(asteroids, Position{X: x, Y: y})
+			} else {
+				field[i] = append(field[i], -1)
+			}
+			x++
+		}
+		y++
+	}
+	return
+}
+
+func CountAsteroidsFromPosition(field [][]int, posX, posY int) (sum int) {
+	duplicate := Copy2DSlice(field)
+	steps := make(map[int]int, 0)
+
+	for y := 0; y < len(duplicate); y++ {
+		for x := 0; x < len(duplicate[y]); x++ {
+			if x == posX && y == posY {
+				continue
+			}
+
+			stepX := x - posX
+			stepY := y - posY
+
+			gcd := GCD(stepY, stepX)
+
+			if gcd == 0 {
+				if stepX > 0 {
+					stepX = 1
+				} else if stepX < 0 {
+					stepX = -1
+				} else if stepY > 0 {
+					stepY = 1
+				} else if stepY < 0 {
+					stepY = -1
+				}
+			} else {
+				stepX, stepY = stepX/gcd, stepY/gcd
+			}
+
+			if v, ok := steps[stepX]; ok && v == stepY {
+				continue
+			}
+			steps[stepX] = stepY
+
+			curX, curY := posX, posY
+			found := false
+			for true {
+				curX += stepX
+				curY += stepY
+
+				if curY < 0 || curX < 0 || curY >= len(duplicate) || curX >= len(duplicate[curY]) {
+					break
+				}
+
+				if duplicate[curY][curX] >= 0 {
+					//log.Printf("(%d,%d) from (%d,%d)", curX, curY, stepX, stepY)
+					if !found {
+						found = true
+						sum++
+					}
+					duplicate[curY][curX] = -2
+				}
+			}
+		}
+	}
+
+	return
+}
+
+func Copy2DSlice(matrix [][]int) (duplicate [][]int) {
+	duplicate = make([][]int, len(matrix))
+	for i := range matrix {
+		duplicate[i] = make([]int, len(matrix[i]))
+		copy(duplicate[i], matrix[i])
+	}
+	return
+}
+
+// greatest common divisor (GCD) via Euclidean algorithm
+func GCD(a, b int) int {
+	for b != 0 {
+		t := b
+		b = a % b
+		a = t
+	}
+
+	if a < 0 {
+		a = a * -1
+	}
+
+	return a
+}