Add day 13 solutions.

common.cr

@@ -1,5 +1,5 @@
 module Enumerable(T)
-  def count_each(others)
+  def count_each
     count_map = {} of T => Int32
     each do |other|
       count_map[other] = (count_map[other]? || 0) + 1

day13.cr

@@ -0,0 +1,120 @@
+require "./common.cr"
+
+lines = File.read("day13_input").split "\n"
+lines.pop
+
+map = lines.map &.chars
+carts = [] of Tuple(Int32, Int32, Char, Char)
+
+map.each_with_index do |line, y|
+  line.each_with_index do |char, x|
+    carts << {x, y, char, 'l'} if char == '>' || char == '<' || char == '^' || char == 'v'
+  end
+end
+
+def next_turn(char)
+  return 'r' if char == 's'
+  return 'l' if char == 'r'
+  return 's'
+end
+
+def turn_dir(char, turn)
+  if turn == 'l'
+    return '<' if char == '^'
+    return 'v' if char == '<'
+    return '>' if char == 'v'
+    return '^' if char == '>'
+  end
+  if turn == 'r'
+    return '>' if char == '^'
+    return '^' if char == '<'
+    return '<' if char == 'v'
+    return 'v' if char == '>'
+  end
+  return char 
+end
+
+def offset(char)
+  case char
+  when '^'
+    {0, -1}
+  when 'v'
+    {0, 1}
+  when '<'
+    {-1, 0}
+  when '>'
+    {1, 0}
+  else
+    {0, 0}
+  end
+end
+
+def turn(cart, turnchar)
+  if turnchar == '/'
+    return '>' if cart == '^'
+    return 'v' if cart == '<'
+    return '^' if cart == '>'
+    return '<'
+  elsif turnchar == '\\'
+    return 'v' if cart == '>'
+    return '<' if cart == '^'
+    return '^' if cart == '<'
+    return '>'
+  end
+  return cart
+end
+
+def simulate(map, carts)
+  crashed = [] of Int32
+  crashed_pos = [] of Tuple(Int32, Int32)
+
+  carts.sort_by! do |cart|
+    x, y, c, t = cart
+    y * 280 + x
+  end
+
+  carts.each_with_index do |cart, index|
+    next if crashed.includes? index
+    x, y, c, t = cart
+
+    # TRUSTED
+    dx, dy = offset(c)
+    x += dx
+    y += dy
+    if map[y][x] == '+'
+      c = turn_dir(c, t)
+      t = next_turn(t)
+    else
+      c = turn(c, map[y][x])
+    end
+    # UNTRUSTED
+
+    carts.each_with_index do |c2, i2|
+      next if crashed.includes? i2
+      next if (c2[0] != x) || (c2[1] != y)
+
+      puts carts
+      crashed << index
+      crashed << i2
+      crashed_pos << {x, y}
+    end
+
+    carts[index] = {x, y, c, t}
+  end
+
+  crashed.sort!.reverse!.uniq!.each do |index|
+    carts.delete_at index
+  end
+
+  unless crashed_pos.empty?
+    puts crashed_pos
+  end
+
+  return carts.size <= 1
+end
+
+count = 0
+while !simulate(map, carts)
+  count += 1
+end
+puts carts[0]?