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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 = 3Output:[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 = 2Output:[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`