Day 10

6 files changed, 222 insertions, 0 deletions

diff --git a/day10/Dockerfile b/day10/Dockerfile
new file mode 100644
index 0000000..e5adcb1
--- /dev/null
+++ b/day10/Dockerfile
@@ -0,0 +1,7 @@
+FROM ruby:2.6.5-slim
+
+WORKDIR /opt
+
+COPY . .
+
+ENTRYPOINT ["./entrypoint"]
diff --git a/day10/Makefile b/day10/Makefile
new file mode 100644
index 0000000..645a112
--- /dev/null
+++ b/day10/Makefile
@@ -0,0 +1,14 @@
+DAY = 10
+
+.PHONY: run clean
+
+run: build
+	docker run -it --rm aoc2019day$(DAY)
+
+build: part* input
+	docker build -t aoc2019day$(DAY) .
+	touch build
+
+clean:
+	docker image rm -f aoc2019day$(DAY)
+	rm -f build
diff --git a/day10/entrypoint b/day10/entrypoint
new file mode 100755
index 0000000..8982d21
--- /dev/null
+++ b/day10/entrypoint
@@ -0,0 +1,13 @@
+#!/bin/bash
+
+if [ -x part1 ] ; then
+	echo -ne "Part 1:\n\t"
+	time ./part1 < input
+fi
+if [ -x part1 -a -x part2 ] ; then
+	echo
+fi
+if [ -x part2 ] ; then
+	echo -ne "Part 2:\n\t"
+	time ./part2 < input
+fi
diff --git a/day10/input b/day10/input
new file mode 100644
index 0000000..43bbd7c
--- /dev/null
+++ b/day10/input
@@ -0,0 +1,26 @@
+.##.#.#....#.#.#..##..#.#.
+#.##.#..#.####.##....##.#.
+###.##.##.#.#...#..###....
+####.##..###.#.#...####..#
+..#####..#.#.#..#######..#
+.###..##..###.####.#######
+.##..##.###..##.##.....###
+#..#..###..##.#...#..####.
+....#.#...##.##....#.#..##
+..#.#.###.####..##.###.#.#
+.#..##.#####.##.####..#.#.
+#..##.#.#.###.#..##.##....
+#.#.##.#.##.##......###.#.
+#####...###.####..#.##....
+.#####.#.#..#.##.#.#...###
+.#..#.##.#.#.##.#....###.#
+.......###.#....##.....###
+#..#####.#..#..##..##.#.##
+##.#.###..######.###..#..#
+#.#....####.##.###....####
+..#.#.#.########.....#.#.#
+.##.#.#..#...###.####..##.
+##...###....#.##.##..#....
+..##.##.##.#######..#...#.
+.###..#.#..#...###..###.#.
+#..#..#######..#.#..#..#.#
diff --git a/day10/part1 b/day10/part1
new file mode 100755
index 0000000..a7859d1
--- /dev/null
+++ b/day10/part1
@@ -0,0 +1,61 @@
+#!/usr/bin/env ruby
+
+input = $stdin.readlines.map(&:strip).map(&:chars)
+              .map{ |l| l.map{ |c| c == "#" } }
+
+H = input.length
+W = input[0].length
+
+def flip_x(arr)
+  arr.map do |x,y|
+    [-x, y]
+  end
+end
+
+def flip_y(arr)
+  arr.map do |x,y|
+    [x, -y]
+  end
+end
+
+def count(grid, x, y, angles)
+  c = 0
+  angles.each do |dx, dy|
+    tx = x
+    ty = y
+    loop do
+      tx += dx
+      ty += dy
+      break if tx < 0 || tx >= W
+      break if ty < 0 || ty >= H
+      if grid[ty][tx] then
+        c += 1
+        break
+      end
+    end
+  end
+  c
+end
+
+angles = []
+(0...W).each do |x|
+  (0...H).each do |y|
+    angles << [x, y] if x.gcd(y) == 1
+  end
+end
+
+angles += flip_x(angles)
+angles += flip_y(angles)
+angles.uniq!
+
+maxcount = 0
+(0...H).each do |y|
+  (0...W).each do |x|
+    if input[y][x] then
+      c = count(input, x, y, angles)
+      maxcount = c if c > maxcount
+    end
+  end
+end
+
+puts maxcount
diff --git a/day10/part2 b/day10/part2
new file mode 100755
index 0000000..f931a36
--- /dev/null
+++ b/day10/part2
@@ -0,0 +1,101 @@
+#!/usr/bin/env ruby
+
+input = $stdin.readlines.map(&:strip).map(&:chars)
+              .map{ |l| l.map{ |c| c == "#" } }
+
+H = input.length
+W = input[0].length
+
+def count(grid, x, y, angles)
+  c = 0
+  angles.each do |dx, dy|
+    tx = x
+    ty = y
+    loop do
+      tx += dx
+      ty += dy
+      break if tx < 0 || tx >= W
+      break if ty < 0 || ty >= H
+      if grid[ty][tx] then
+        c += 1
+        break
+      end
+    end
+  end
+  c
+end
+
+def rotate(n, arr)
+  arr.map do |x, y|
+    case n
+    when 1
+      [-y, x]
+    when 2
+      [-x, -y]
+    when 3
+      [y, -x]
+    end
+  end
+end
+
+def coords_of(n, grid, x, y, angles)
+  c = 0
+  loop do
+    tx = x
+    ty = y
+    angles.each do |dx, dy|
+      s = 1
+      loop do
+        tx = x + s*dx
+        ty = y + s*dy
+        break if tx < 0 || tx >= W
+        break if ty < 0 || ty >= H
+        if grid[ty][tx] then
+          c += 1
+          return [tx, ty] if c == 200
+          break
+        else
+          s += 1
+        end
+      end
+    end
+  end
+end
+
+angles = []
+(0...W).each do |x|
+  (0...H).each do |y|
+    angles << [x, -y] if x.gcd(y) == 1
+  end
+end
+
+angles.sort! do |a,b|
+  b[0].to_f/b[1] <=> a[0].to_f/a[1]
+end
+
+angles.shift
+
+angles = angles +
+         rotate(1, angles) +
+         rotate(2, angles) +
+         rotate(3, angles)
+
+maxcount = 0
+stationx = nil
+stationy = nil
+(0...H).each do |y|
+  (0...W).each do |x|
+    if input[y][x] then
+      c = count(input, x, y, angles)
+      if c > maxcount
+        maxcount = c
+        stationx = x
+        stationy = y
+      end
+    end
+  end
+end
+
+asteroid200 = coords_of(200, input, stationx, stationy, angles)
+
+puts (100 * asteroid200[0]) + asteroid200[1]