adventofcode/03dec/main.go

package main

import (
	"fmt"
	"os"
	"strconv"
)

const (
	// directions
	W = iota
	N
	E
	S
)

var (
	// current value
	cur int
	// current position
	x, y int
	// current direction
	dir int
	// grid bounds
	xmax, xmin, ymax, ymin int
)

func main() {
	n, err := strconv.Atoi(os.Args[1])
	if err != nil {
		os.Exit(1)
	}
	// move current position in grid and compute change direction, expand grid
	for cur < n {
		nextMove()
		// fmt.Println(cur, x, y)
	}
	// distance to position
	fmt.Println(Abs(x) + Abs(y))
}

func nextMove() {
	if cur == 0 {
		dir = S
	} else {
		x1, y1 := dirMove()
		if outOfBound(x1, y1) {
			changeDir()
			x1, y1 = dirMove()
		}
		x, y = x1, y1
	}
	cur++
}

func dirMove() (int, int) {
	switch dir {
	case W:
		return x - 1, y
	case N:
		return x, y + 1
	case E:
		return x + 1, y
	case S:
		return x, y - 1
	default:
		return x, y
	}
}
func outOfBound(x1 int, y1 int) bool {
	return x1 > xmax || x1 < xmin || y1 > ymax || y1 < ymin
}
func changeDir() {
	switch dir {
	case W:
		dir = S
		ymin--
	case N:
		dir = W
		xmin--
	case E:
		dir = N
		ymax++
	case S:
		dir = E
		xmax++
	}
}
func Abs(n int) int {
	if n < 0 {
		return -n
	}
	return n
}