Gray Codes

gray.go

package main

import (
	"fmt"
	"math"
)

func main() {
	fmt.Printf("%010b", gray(10))
}

// from https://en.wikipedia.org/wiki/Gray_code
// "... an ordering of the binary numeral system such that two successive values differ in only one bit (binary digit)"

func gray(n int) []int {
	if n == 0 {
		return []int{}
	}
	if n == 1 {
		return []int{0b0, 0b1}
	}
	prev := gray(n-1)
	left, right := make([]int, pow2(n-1)), make([]int, pow2(n-1))
	for i, c := range prev {
		left[i] = c << 1
		right[len(right)-i-1] = left[i] | 0b1
	}
	return append(left, right...)
}

func pow2(n int) int {
	return int(math.Exp2(float64(n)))
}