2016-day23: easiest assembly manual understanding so far

2016/day23/main.go

@@ -0,0 +1,143 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"regexp"
+	"strings"
+
+	"github.com/alexchao26/advent-of-code-go/cast"
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+func main() {
+	var part int
+	flag.IntVar(&part, "part", 1, "part 1 or 2")
+	flag.Parse()
+	fmt.Println("Running part", part)
+
+	ans := assemblyComputer(util.ReadFile("./input.txt"), part)
+	fmt.Println("Output:", ans)
+}
+
+func assemblyComputer(input string, part int) int {
+	instructions := strings.Split(input, "\n")
+	registers := map[string]int{}
+	var instIndex int
+
+	registers["a"] = 7
+	if part == 2 {
+		registers["a"] = 12
+	}
+
+	for instIndex < len(instructions) {
+		// uncomment this to print out the instruction set and see how it's changed
+		// fmt.Println(instIndex)
+		// for in, i := range instructions {
+		// 	fmt.Println(in, i)
+		// }
+		// fmt.Println()
+
+		inst := instructions[instIndex]
+		parts := strings.Split(inst, " ")
+
+		// My instruction list gets transformed into this
+		// all jump instructions can be optimized, in particular the ones
+		// tagged here b/c they jump over another jump instruction
+		//   effectively becoming multiplication steps
+		// 0 cpy a b
+		// 1 dec b
+		// 2 cpy a d
+		// 3 cpy 0 a
+		// 4 cpy b c
+		// 5 inc a
+		// 6 dec c
+		// 7 jnz c -2
+		// 8 dec d
+		// 9 jnz d -5 // <-
+		// 10 dec b
+		// 11 cpy b c
+		// 12 cpy c d
+		// 13 dec d
+		// 14 inc c
+		// 15 jnz d
+		// 16 tgl c
+		// 17 cpy -16 c
+		// 18 cpy 1 c
+		// 19 cpy 89 c
+		// 20 cpy 77 d
+		// 21 inc a
+		// 22 dec d
+		// 23 jnz d
+		// 24 dec c
+		// 25 jnz c -5 // <-
+
+		// Hard coded multiplication skippers
+		if inst == "jnz d -5" && instructions[instIndex-1] == "dec d" &&
+			instructions[instIndex-2] == "jnz c -2" {
+			registers["a"] += registers["b"] * registers["d"]
+			registers["c"] = 0
+			registers["d"] = 0
+		}
+
+		if inst == "jnz c -5" && instructions[instIndex-1] == "dec c" {
+			registers["a"] += 77 * registers["c"]
+			registers["c"] = 0
+			registers["d"] = 0
+		}
+
+		switch parts[0] {
+		case "cpy":
+			valX := parseValueOrRegister(registers, parts[1])
+			registers[parts[2]] = valX
+			instIndex++
+		case "inc":
+			registers[parts[1]]++
+			instIndex++
+		case "dec":
+			registers[parts[1]]--
+			instIndex++
+		case "jnz":
+			valX := parseValueOrRegister(registers, parts[1])
+			if valX != 0 {
+				valY := parseValueOrRegister(registers, parts[2])
+				instIndex += valY
+			} else {
+				instIndex++
+			}
+		case "tgl":
+			// valX is an offset
+			valX := parseValueOrRegister(registers, parts[1])
+			indexToMod := instIndex + valX
+			if indexToMod < len(instructions) {
+				instToModParts := strings.Split(instructions[indexToMod], " ")
+				var newType string
+				if len(instToModParts) == 2 {
+					newType = "inc"
+					if instToModParts[0] == "inc" {
+						newType = "dec"
+					}
+				} else if len(instToModParts) == 3 {
+					newType = "jnz"
+					if instToModParts[0] == "jnz" {
+						newType = "cpy"
+					}
+				}
+				instToModParts[0] = newType
+				instructions[indexToMod] = strings.Join(instToModParts, " ")
+			}
+			instIndex++
+		default:
+			panic("unhanded instruction type " + parts[0])
+		}
+	}
+
+	return registers["a"]
+}
+
+func parseValueOrRegister(registers map[string]int, part string) int {
+	if regexp.MustCompile("[0-9]").MatchString(part) {
+		return cast.ToInt(part)
+	}
+	return registers[part]
+}

2016/day23/main_test.go

@@ -0,0 +1,35 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+var example = `cpy 2 a
+tgl a
+tgl a
+tgl a
+cpy 1 a
+dec a
+dec a`
+
+func Test_part1(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		part  int
+		want  int
+	}{
+		{"example", example, 1, 3},
+		{"actual", util.ReadFile("input.txt"), 1, 11893},
+		{"actual", util.ReadFile("input.txt"), 2, 479008453},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := assemblyComputer(tt.input, tt.part); got != tt.want {
+				t.Errorf("assemblyComputer() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}