Gray Code

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

i ^ (i >> 1)

public List<Integer> grayCode(int n) {
    List<Integer> ans = new ArrayList<>();
    for (int i = 0; i < (1<<n); i++) {
        ans.add(i ^ (i>>1));
    }
    return ans;
}