adventofcode2021/2-1/main.go

package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
)

type Instruction struct {
	instr int // forward = 0, up = 1, down = 2
	value int
}

func (in *Instruction) execute(x, depth int) (int, int) {
	switch in.instr {
	case 0: // Forward
		x += in.value
	case 1: // Up
		depth -= in.value
	case 2: // Down
		depth += in.value
	}

	return x, depth
}

func newInstruction(str string, val int) Instruction {
	instr := 0

	switch str {
	case "forward":
		instr = 0
	case "up":
		instr = 1
	case "down":
		instr = 2
	}

	in := Instruction{
		instr: instr,
		value: val,
	}
	return in
}

func parseInstruction(instruction string) (Instruction, error) {
	instr := strings.Split(instruction, " ")
	part1 := instr[0]
	part2, err := strconv.Atoi(instr[1])
	if err != nil {
		return Instruction{}, err
	}

	return newInstruction(part1, part2), nil
}

func readInput(filename string) ([]Instruction, error) {
	file, err := os.Open(filename)
	if err != nil {
		return nil, err
	}
	defer file.Close()

	scanner := bufio.NewScanner(file)
	instructions := make([]Instruction, 0)

	for scanner.Scan() {
		in, err := parseInstruction(scanner.Text())
		if err != nil {
			return nil, err
		}
		instructions = append(instructions, in)
	}

	return instructions, nil
}

func main() {
	ins, err := readInput("input")
	if err != nil {
		fmt.Printf("%s", err.Error())
		return
	}

	xPos := 0
	depth := 0

	for i := 0; i < len(ins); i++ {
		xPos, depth = ins[i].execute(xPos, depth)
	}

	fmt.Printf("X is now: %d\nDepth is now: %d\nMultiplied is: %d", xPos, depth, (xPos * depth))
}