Circular Permutation in Binary Representation

Problem

Given 2 integers n and start. Your task is return any permutation p of (0,1,2.....,2^n -1) such that :

p[0] = start
p[i] and p[i+1] differ by only one bit in their binary representation.
p[0] and p[2^n -1] must also differ by only one bit in their binary representation.

Example 1:

Input: n = 2, start = 3
Output: [3,2,0,1]
Explanation: The binary representation of the permutation is (11,10,00,01). 
All the adjacent element differ by one bit. Another valid permutation is [3,1,0,2]

Example 2:

Input: n = 3, start = 2
Output: [2,6,7,5,4,0,1,3]
Explanation: The binary representation of the permutation is (010,110,111,101,100,000,001,011).

Constraints:

1 <= n <= 16
0 <= start < 2 ^ n

Solution (Java)

class Solution {
    public List<Integer> circularPermutation(int n, int start) {

        List<Integer> l1 = new ArrayList<>();
        for (int i = 0; i < (1 << n); i++) {
            l1.add(start ^ (i ^ (i >> 1)));
        }
        return l1;
    }
}

Explain:

nope.

Complexity:

Time complexity : O(n).
Space complexity : O(n).