day10 p2

day10/day10.jl

@@ -2,7 +2,7 @@
 
 using Test
 
-struct Instruction
+mutable struct Instruction
   cycles :: UInt
   add    :: Int
 end
@@ -18,7 +18,7 @@ function parse_instruction_line(line)
   end
 end
 
-function execute_program(io; end_cycle=220)
+function signal_strength_sum(io; end_cycle=220)
   X :: Int = 1
   cycle :: Int = 1
   signal_strength_sum :: Int = 0
@@ -43,10 +43,48 @@ function execute_program(io; end_cycle=220)
   return signal_strength_sum
 end
 
+function get_crt(io; end_cycle=240)
+  X :: Int = 2 # Note: add 1 to simplify 1-based indexing
+  pending_instruction :: Union{Instruction, Nothing} = nothing
+  screen = fill('.', (Int(ceil(end_cycle / 40)), 40))
+  nrows, ncols = size(screen)
+  for i in 1:nrows
+    for j in 1:ncols
+      if abs(X - j) <= 1
+        screen[i, j] = "#"[1]
+      else 
+        screen[i, j] = '.'
+      end
+
+      if pending_instruction === nothing
+        if eof(io)
+          continue
+        end
+        inst = parse_instruction_line(readline(io))
+        pending_instruction = inst
+      end
+      pending_instruction.cycles -= 1
+      if pending_instruction.cycles == 0
+        X += pending_instruction.add
+        pending_instruction = nothing
+      end
+    end
+  end
+  return join(reduce(*, screen, dims=2, init=""), "\n")
+end
+
 function test()
   @testset "signal strength sum" verbose=true begin
-    @test execute_program("example.txt") == 13140
-    @test execute_program("input.txt") == 13220
+    @test signal_strength_sum("example.txt") == 13140
+    @test signal_strength_sum("input.txt") == 13220
+  end
+  @testset "crt test" verbose=true begin
+    open("example.txt") do io
+      @test get_crt(io) == chomp(read("example_crt.txt", String))
+    end
+    open("input.txt") do io
+      @test get_crt(io) == chomp(read("input_crt.txt", String))
+    end
   end
 end
 
@@ -56,7 +94,10 @@ function main()
   else
     infile = ARGS[1]
     println("infile = ", infile)
-    println("signal strength sum = ", execute_program(infile))
+    println("signal strength sum = ", signal_strength_sum(infile))
+    open(infile, "r") do io
+      println(get_crt(io))
+    end
   end
 end
 

day10/example_crt.txt

@@ -0,0 +1,6 @@
+##..##..##..##..##..##..##..##..##..##..
+###...###...###...###...###...###...###.
+####....####....####....####....####....
+#####.....#####.....#####.....#####.....
+######......######......######......####
+#######.......#######.......#######.....

day10/input_crt.txt

@@ -0,0 +1,6 @@
+###..#..#..##..#..#.#..#.###..####.#..#.
+#..#.#..#.#..#.#.#..#..#.#..#.#....#.#..
+#..#.#..#.#..#.##...####.###..###..##...
+###..#..#.####.#.#..#..#.#..#.#....#.#..
+#.#..#..#.#..#.#.#..#..#.#..#.#....#.#..
+#..#..##..#..#.#..#.#..#.###..####.#..#.