Add day 11 solution.

day11.cr

@@ -0,0 +1,64 @@
+map = Array(Array(Array(Int32))).new(301) { |i| Array(Array(Int32)).new(301) { |j| Array(Int32).new(301, 0) } }
+
+pairs = (1..300).to_a.product (1..300).to_a
+(1..300).each do |y|
+  (1..300).each do |x|
+    rack_id = x + 10
+    level = rack_id * y
+    level += 3463
+    level *= rack_id
+    digit = (level / 100) % 10
+    digit -= 5
+
+    map[x][y][1] = digit
+  end
+end
+
+def square_score(powers, coord, size)
+  x, y = coord
+  total = 0
+  half = size / 2
+
+  total = powers[x][y][half] +
+    powers[x][y + half][half] +
+    powers[x + half][y][half] +
+    powers[x + half][y + half][half]
+
+  if size.odd?
+    size.times do |i|
+      total += powers[x + size - 1][y + i][1]
+      total += powers[x + i][y + size - 1][1]
+    end
+    total -= powers[x + size - 1][y + size - 1][1]
+  end
+
+  powers[x][y][size] = total
+  return total
+end
+
+def max_score(powers, pairs, size = 3)
+  possible_squares = (1..300 - size + 1).to_a
+  possible_pairs = possible_squares.product possible_squares
+  
+  possible_pairs.max_by do |pair|
+    x, y = pair
+    score = square_score(powers, pair, size)
+  end
+end
+
+puts max_score(map, pairs, 2)
+puts max_score(map, pairs, 3)
+
+max = -1000
+max_pair = nil
+297.times do |i|
+  pair = max_score(map, pairs, i + 4)
+  score = square_score(map, pair, i + 4)
+  if score > max
+    max = score
+    max_pair = { pair, i + 4 }
+  else
+    break
+  end
+end
+puts max_pair