Add J solution for day 5.

day1.ijs

@@ -0,0 +1,3 @@
+c =. > 0 ". each cutopen 1!:1 < jpath '~/projects/AoC/2020/year2020day1.txt.cache'
+>./,(c*/c)*2020=c+/c
+>./,(c*/c*/c)*2020=c+/c+/c

day2.ijs

@@ -0,0 +1,6 @@
+r =: >"1 cut each cutopen 1!:1 < jpath '~/projects/AoC/2020/year2020day2.txt.cache'
+rs =: >0".each'-'cut"1>(0}"1 r)
+cs =: 0{"1>1{"1 r
+ss =: 2{"1 r
++/1>**/|:rs-+/"1 cs=>ss
++/1=+/|:(rs-1){"1 cs=>ss

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)}"

day24.cr

@@ -0,0 +1,78 @@
+require "advent"
+
+INPUT = input(2020, 24).lines.map &.tiles.map { |t| MATCHES[t] }
+MATCHES = { "se" => {0.5, -1.0}, "sw" => {-0.5, -1.0}, "ne" => {0.5, 1.0}, "nw" => {-0.5, 1.0}, "e" => {1.0, 0.0}, "w" => {-1.0, 0.0} }
+
+class String
+  def tiles
+    i = 0
+    tiles = [] of String
+    while i < size
+      if self[i] == 's' || self[i] == 'n'
+        tiles << self[i..i+1] 
+        i += 2
+      else
+        tiles << self[i..i]
+        i += 1
+      end
+    end
+    tiles
+  end
+end
+
+class Array(T)
+  def pos
+    curr = {0.0, 0.0}
+    each do |c|
+      curr = curr.add c
+    end
+    curr
+  end
+end
+
+def part1(input)
+  counts = Hash({Float64,Float64}, Int32).new(0)
+  input.each do |i|
+    counts[i.pos] += 1
+  end
+  counts.count &.[1].%(2).==(1)
+end
+
+struct Tuple(*T)
+  def neighbors
+    MATCHES.values.map &.add(self)
+  end
+end
+
+def part2(input)
+  state = Hash({Float64,Float64}, Bool).new(false)
+  counts = Hash({Float64,Float64}, Int32).new(0)
+
+  input.each do |i|
+    state[i.pos] ^= true
+  end
+
+  100.times do |i|
+    counts.clear
+    state.each do |t, f|
+      next unless f
+      t.neighbors.each do |n|
+        counts[n] += 1
+      end
+    end
+
+    new_state = state.clone.clear
+    state.each do |k, v|
+      next unless v
+      new_state[k] = !(counts[k] == 0 || (counts[k] > 2))
+    end
+    counts.each do |k, v|
+      new_state[k] = true if (!state[k]) && v == 2
+    end
+    state = new_state
+  end
+  state.count &.[1]
+end
+
+puts part1(INPUT.clone)
+puts part2(INPUT.clone)

day3.ijs

@@ -0,0 +1,5 @@
+r =: > cutopen 1!:1 < jpath '~/projects/AoC/2020/year2020day3.txt.cache'
+rn =: 4 : '+/''#''=((#|:y)|x*i.#y){"0 1 y'
+rnx =: 3 : '(1{y) rn 0{"2((0{-y)]\r)'
+rnx 1 3
+*/ rnx"1 (_2 [\ 1 1 1 3 1 5 1 7 2 1)

day5.ijs

@@ -0,0 +1,4 @@
+bs2n =: 3 : '+/ "1(|.*/\(1,(_1+#y)$2)) *"(1) 0 "."0 y'
+ns =: bs2n "1 'F0B1L0R1' charsub > cutopen 1!:1 < jpath '~/projects/AoC/2020/year2020day5.txt.cache'
+>./ns
+(<./ns)+I.-.((<./ns)+i.#ns)e.ns