LeetCode89 Gray Code

LeetCode89 Gray Code

問題來源LeetCode89

問題描述

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.

問題分析

Gray Code（格雷碼）具體的用途可以看一下百度百科。一般格雷碼有專門的迭代公式。

n位格格雷碼=

最高位0 + n-1位格雷碼的順序 +

最高位1 + n-1位格雷碼的逆序。

最高位0不影響大小，最高位1可以通過位運算來實現。1 << (n-1)

代碼如下

public List<Integer> grayCode(int n) {
        List<Integer> result = new ArrayList<>();
    result.add(0);
    if(n==0){
        return result;
    }
    List<Integer> tmp = grayCode(n-1);
    int addNumber = 1 << (n-1);
    result = new ArrayList<Integer>(tmp);
    for(int i=tmp.size()-1;i>=0;i--) {
        result.add(addNumber + tmp.get(i));
    }
    return result;
}

LeetCode學習筆記持續更新

GitHub地址 https://github.com/yanqinghe/leetcode

CSDN博客地址 http://blog.csdn.net/yanqinghe123/article/category/7176678