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# 1238. Circular Permutation in Binary Representation

<https://leetcode.com/problems/circular-permutation-in-binary-representation>

## Description

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`

## ac

```java
```