Add day 23.

day23.cr

@@ -0,0 +1,117 @@
+require "advent"
+
+input = input(2020, 23).lines[0].chars.map &.to_i32
+
+class Array(T)
+  def get(i)
+    self[i % size]
+  end
+
+  def del(i)
+    delete_at(i % size)
+  end
+end
+
+class Node
+  property next : Node
+  property int : Int32
+
+  def initialize(@int, @next)
+  end
+
+  def insert(other : Node, n = 1)
+    set_next = other
+    (n-1).times { set_next = set_next.@next }
+    set_next.next = @next
+    @next = other
+  end
+
+  def remove(n = 1)
+    curr = self
+    to_return = self.next
+    n.times { curr = curr.@next }
+    @next = curr.@next
+    to_return
+  end
+
+  def find(n)
+    start = self
+    while start.int != n
+      start = start.next
+    end
+    return start
+  end
+  
+  def to_s(n)
+    return "" if n < 0
+    return "#{@int} -> #{@next.to_s(n-1)}"
+  end
+
+  def includes?(n, count)
+    return false if count <= 0
+    return @int == n || @next.includes?(n, count-1)
+  end
+end
+
+class Cups
+  getter size : Int32
+  getter head : Node
+
+  def initialize(list : Array(Int32))
+    @cache = {} of Int32 => Node
+    h = list.delete_at(0)
+    temp = uninitialized Node
+    @cache[h] = @head = Node.new(h, temp)
+    @size = list.size
+    @local_min = list.min.as(Int32)
+    @local_max = list.max.as(Int32)
+    @head.next = @head
+    curr = @head
+    list.each do |n|
+      @cache[n] = new = Node.new(n, curr.next)
+      curr.insert(new)
+      curr = new
+    end
+  end
+  
+  def to_s
+    @head.to_s(@size)
+  end
+
+  def step
+    first = @head
+    after = first.remove(3)
+    m = first.int - 1
+    while after.includes?(m, 3) || m < @local_min
+      m = (m < @local_min) ? @local_max : (m - 1)
+    end
+    @cache[m].insert(after, 3)
+    @head = @head.next
+  end
+end
+
+def play(input, count)
+  cups = Cups.new input
+  count.times { |n| cups.step }
+  cups
+end
+
+def part1(input)
+  cups = play(input.clone, 100)
+  cups.head.find(1).next.to_s(cups.size - 1).gsub(" -> ", "")
+end
+
+def part2(input)
+  list = input.clone
+  max = input.max
+  (1000000 - input.size).times do
+    max += 1
+    list << max
+  end
+  cups = play(list, 10000000)
+  one = cups.head.find(1)
+  one.next.int.to_i64 * one.next.next.int
+end
+
+puts "Part 1: #{part1(input)}"
+puts "Part 2: #{part2(input)}"