Day 3: spiral

03dec/main.go

@@ -0,0 +1,94 @@
+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
+}