http://cslai.coolsilon.com/2014/09/12/spiraling-number/

spiral.go

package main

import "fmt"

func spiral(max_x int, max_y int) {
	var n, x, y, xdir, ydir int
	xdir = 1

	var matrix = make([][]int, max_y)
	for i := range matrix {
		matrix[i] = make([]int, max_x)
	}

	for {
		n++
		matrix[y][x] = n
		x, y = x+xdir, y+ydir

		if x < 0 || x >= max_x || y < 0 || y >= max_y || matrix[y][x] > 0 {
			x, y = x-xdir, y-ydir
			xdir, ydir = -ydir, xdir
			x, y = x+xdir, y+ydir

			if matrix[y][x] != 0 {
				break
			}
		}
	}

	for y = range matrix {
		for x = range matrix[y] {
			fmt.Printf("%2d ", matrix[y][x])
		}
		fmt.Println()
	}
}

func main() {
	spiral(5, 5)
}