Add day 8 solution.

2020/day08.go

@@ -0,0 +1,101 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"strconv"
+	"strings"
+
+	"git.annabunch.es/annabunches/adventofcode/2020/lib/fileutils"
+)
+
+type Instruction struct {
+	Operation string
+	Operand   int
+}
+
+func parseInstruction(input string) Instruction {
+	data := strings.Split(input, " ")
+	op := data[0]
+	operand, err := strconv.Atoi(strings.TrimPrefix(data[1], "+"))
+	if err != nil {
+		log.Panicf(err.Error())
+	}
+	return Instruction{
+		Operation: op,
+		Operand:   operand,
+	}
+}
+
+func executeInstruction(ins Instruction, ip, acc *int, history map[int]bool) {
+	history[*ip] = true
+	switch ins.Operation {
+	case "acc":
+		*acc += ins.Operand
+		*ip++
+	case "jmp":
+		*ip += ins.Operand
+	case "nop":
+		*ip++
+	}
+}
+
+func executeProgram(instructions []Instruction) (int, bool) {
+	ip := 0
+	acc := 0
+	history := make(map[int]bool)
+
+	for ip < len(instructions) {
+		if _, found := history[ip]; found {
+			// detect infinite loop and return
+			return acc, true
+		}
+		executeInstruction(instructions[ip], &ip, &acc, history)
+	}
+
+	return acc, false
+}
+
+func main() {
+	step := os.Args[1]
+	values := fileutils.InputParserStrings(os.Args[2])
+
+	instructions := make([]Instruction, 0)
+
+	for _, line := range values {
+		if line == "" {
+			continue
+		}
+		ins := parseInstruction(line)
+		instructions = append(instructions, ins)
+	}
+
+	switch step {
+	case "1":
+		ret, loop := executeProgram(instructions)
+		if loop {
+			fmt.Println("Loop detected. Last ACC value:", ret)
+		}
+
+	case "2":
+		for i, ins := range instructions {
+			if ins.Operation == "jmp" || ins.Operation == "nop" {
+				newInstructions := make([]Instruction, len(instructions))
+				copy(newInstructions, instructions)
+				switch ins.Operation {
+				case "jmp":
+					newInstructions[i].Operation = "nop"
+				case "nop":
+					newInstructions[i].Operation = "jmp"
+				}
+				ret, loop := executeProgram(newInstructions)
+
+				if !loop {
+					fmt.Println(ret)
+					break
+				}
+			}
+		}
+	}
+}