Add solution for 2021 day 11

2021/README.md

@@ -3,7 +3,7 @@
 ## Progress
 
 | Day | Part 1 | Part 2 | Language  |
-| :-: | :----: | :----: | :------- |
+| :-: | :----: | :----: | :-------- |
 | 01  |   ✓    |   ✓    | [Ruby]    |
 | 02  |   ✓    |   ✓    | [Ada]     |
 | 03  |   ✓    |   ✓    | [Perl]    |
@@ -14,7 +14,7 @@
 | 08  |   ✓    |   ✓    | [C#]      |
 | 09  |   ✓    |   ✓    | [C]       |
 | 10  |   ✓    |   ✓    | [OCaml]   |
-| 11  |        |        |          |
+| 11  |   ✓    |   ✓    | [Crystal] |
 | 12  |        |        |           |
 | 13  |        |        |           |
 | 14  |        |        |           |
@@ -46,3 +46,4 @@
 [c#]: https://docs.microsoft.com/en-us/dotnet/csharp/
 [c]: http://www.open-std.org/jtc1/sc22/wg14
 [ocaml]: https://ocaml.org
+[crystal]: https://crystal-lang.org

2021/day-11/Justfile

@@ -0,0 +1,6 @@
+@part PART INPUT_FILE="inputs/puzzle.txt":
+    crystal build --error-trace part_{{PART}}.cr
+    ./part_{{PART}} {{INPUT_FILE}}
+
+clean:
+    rm -f part_one part_two

2021/day-11/common.cr

@@ -0,0 +1,70 @@
+alias OctopusMap = Array(Array(Int32))
+alias FlashMap = Array(Array(Bool))
+
+SURROUNDING = [-1, 0, 1]
+  .repeated_permutations(2)
+  .reject { |v| v == [0, 0] }
+  .map { |v| Tuple(Int32, Int32).from(v) }
+  .to_set
+
+def parse_file(path : String) : OctopusMap
+  File.read_lines(path, chomp: true).map &.chars.map(&.to_i)
+end
+
+def print_map(octopi : OctopusMap)
+  puts "-" * octopi.first.size
+  octopi.each do |row|
+    puts row
+  end
+  puts "-" * octopi.first.size
+end
+
+def flash(x : Int32, y : Int32, octopi : OctopusMap, flashes : FlashMap) : Int32
+  flashes[y][x] = true
+  octopi[y][x] = 0
+
+  return 1 + mark_surrounding(x, y, octopi, flashes) do |nx, ny|
+    next 0 if flashes[ny][nx]
+    next flash(nx, ny, octopi, flashes) if octopi[ny][nx] > 9
+    0
+  end
+end
+
+def mark_surrounding(x : Int32, y : Int32, octopi : OctopusMap, flashes : FlashMap) : Int32
+  valid_surrounding = SURROUNDING.reject do |(dx, dy)|
+    val = false
+    val ||= dx == -1 if x == 0
+    val ||= dx == 1 if x == octopi.first.size - 1
+    val ||= dy == -1 if y == 0
+    val ||= dy == 1 if y == octopi.size - 1
+    val
+  end
+
+  return valid_surrounding.sum do |(dx, dy)|
+    octopi[y + dy][x + dx] += 1 unless flashes[y + dy][x + dx]
+    yield x + dx, y + dy
+  end
+end
+
+def generation(octopi : OctopusMap, flashes : FlashMap) : Int32
+  gen_flash_count = 0
+
+  octopi.each_with_index do |row, y|
+    row.each_with_index do |_, x|
+      next if flashes[y][x]
+      octopi[y][x] += 1
+      gen_flash_count += flash(x, y, octopi, flashes) if octopi[y][x] > 9
+    end
+  end
+
+  gen_flash_count
+end
+
+def generations(steps : Int32, octopi : OctopusMap, flashes : FlashMap, flash_count : Int32) : Int32
+  return flash_count if steps == 0
+
+  flash_count += generation(octopi, flashes)
+
+  flashes = octopi.map &.map { false }
+  return generations(steps - 1, octopi, flashes, flash_count)
+end

2021/day-11/inputs/puzzle.txt

@@ -0,0 +1,10 @@
+4134384626
+7114585257
+1582536488
+4865715538
+5733423513
+8532144181
+1288614583
+2248711141
+6415871681
+7881531438

2021/day-11/inputs/sample.txt

@@ -0,0 +1,10 @@
+5483143223
+2745854711
+5264556173
+6141336146
+6357385478
+4167524645
+2176841721
+6882881134
+4846848554
+5283751526

2021/day-11/part_one.cr

@@ -0,0 +1,10 @@
+require "./common"
+
+def main(path)
+  octopi = parse_file(path)
+  flashes = octopi.map &.map { false }
+
+  puts generations(100, octopi, flashes, 0)
+end
+
+main(ARGV.first)

2021/day-11/part_two.cr

@@ -0,0 +1,18 @@
+require "./common"
+
+def main(path)
+  octopi = parse_file(path)
+
+  req_flashes = octopi.size * octopi.first.size
+
+  (1..).each do |generation|
+    flashes = octopi.map &.map { false }
+    gen_flashes = generation(octopi, flashes)
+    if gen_flashes == req_flashes
+      puts generation
+      break
+    end
+  end
+end
+
+main(ARGV.first)

README.md

@@ -8,4 +8,4 @@
 -   [2018](2018/README.md) (0% completed)
 -   [2019](2019/README.md) (0% completed)
 -   [2020](2020/README.md) (16% completed)
--   [2021](2021/README.md) (40% completed)
+-   [2021](2021/README.md) (44% completed)