089.go

package p089

/**
The gray code is a binary numeral system where two successive values differ in only one bit.

Given a non-negative integer n representing the total number of bits in the code, print the sequence of gray code. A gray code sequence must begin with 0.

For example, given n = 2, return [0,1,3,2]. Its gray code sequence is:

00 - 0
01 - 1
11 - 3
10 - 2
Note:
For a given n, a gray code sequence is not uniquely defined.

For example, [0,2,3,1] is also a valid gray code sequence according to the above definition.

For now, the judge is able to judge based on one instance of gray code sequence. Sorry about that.
*/

func grayCode(n int) []int {
	res := make([]int, 1<<uint(n))
	for i := 0; i < n; i++ {
		diff := 1 << uint(i)
		lo := diff - 1
		hi := diff
		for lo >= 0 {
			res[hi] = res[lo] | diff
			lo--
			hi++
		}
	}
	return res
}