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LeetCode:Gray Code 题解

题目描述:

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

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.

 

考察位操作

从题目中例子可以发现这么一个规律:

假设结果数组为B,原始数组为A,则有:

B[i]  = A[i] ^ (A[i]>>1).  

例如 : A[3] =3     
       B[3] = 3^(3>>1) 
            = 011^001 
            = 010 = 2

 

解法如下:

 1 class Solution {
 2 public:
 3     vector<int> grayCode(int n) {
 4         int len = pow(2.0,n),i,a;
 5         vector<int> vi;
 6         for(i=0;i<len;i++)
 7         {
 8             a= i^(i>>1);
 9             vi.push_back(a);
10         }
11         return vi;
12     }
13 };