Implementation for 21b

challenge/day21/b.go

@@ -0,0 +1,61 @@
+package day21
+
+import (
+	"fmt"
+
+	"github.com/nlowe/aoc2019/intcode"
+	"github.com/nlowe/aoc2019/intcode/input"
+	"github.com/nlowe/aoc2019/intcode/output"
+
+	"github.com/nlowe/aoc2019/challenge"
+	"github.com/spf13/cobra"
+)
+
+var B = &cobra.Command{
+	Use:   "21b",
+	Short: "Day 21, Problem B",
+	Run: func(_ *cobra.Command, _ []string) {
+		fmt.Printf("Answer: %d\n", b(challenge.FromFile()))
+	},
+}
+
+const cmdRun = "RUN"
+
+func b(challenge *challenge.Input) int {
+	in := make(chan string)
+	cpu, out := intcode.NewCPUForProgram(<-challenge.Lines(), input.ASCIIWrapper(in))
+
+	go cpu.Run()
+
+	dmg := 0
+	wg := output.Each(out, func(i int) {
+		if i < 255 {
+			fmt.Print(string(rune(i)))
+		}
+		dmg = i
+	})
+
+	// The springdroid jumps 4 spaces at t time, so there are only 3 cases to check
+	// We need to initiate a jump when
+	// * the very next tile is a hole (!A)
+	// * AND All Of
+	//   * There is a hole 3 tiles out (jump as early as possible, !C) AND
+	//   * If we jump now we won't fall (D) AND
+	//   * If we jump *again* immediately afterwards, we won't fall (H)
+	// * OR Both
+	//   * The 2nd tile out is a hole that we couldn't make last turn (so !B) AND
+	//   * The 4th tile is solid (so we have something to land on, so D)
+	// !A || (!C && D && H) || (!B && D)
+	in <- "NOT C J"
+	in <- "AND D J"
+	in <- "AND H J"
+	in <- "NOT B T"
+	in <- "AND D T"
+	in <- "OR T J"
+	in <- "NOT A T"
+	in <- "OR T J"
+	in <- cmdRun
+
+	wg.Wait()
+	return dmg
+}

main.go

@@ -4,8 +4,6 @@ import (
 	"fmt"
 	"time"
 
-	"github.com/nlowe/aoc2019/challenge/day21"
-
 	"github.com/nlowe/aoc2019/challenge/day1"
 	"github.com/nlowe/aoc2019/challenge/day10"
 	"github.com/nlowe/aoc2019/challenge/day11"
@@ -19,6 +17,7 @@ import (
 	"github.com/nlowe/aoc2019/challenge/day19"
 	"github.com/nlowe/aoc2019/challenge/day2"
 	"github.com/nlowe/aoc2019/challenge/day20"
+	"github.com/nlowe/aoc2019/challenge/day21"
 	"github.com/nlowe/aoc2019/challenge/day3"
 	"github.com/nlowe/aoc2019/challenge/day4"
 	"github.com/nlowe/aoc2019/challenge/day5"
@@ -83,7 +82,7 @@ func init() {
 		day18.A, day18.B,
 		day19.A, day19.B,
 		day20.A, day20.B,
-		day21.A,
+		day21.A, day21.B,
 	)
 
 	flags := rootCmd.PersistentFlags()