[leetCode] Gray Code

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

when n=3:
000

001

011

010

110

111

101

100

所以 n=3的格雷码 = n=2的编码 + (1<<2+n=2的转置)

class Solution {
public:
vector<int> grayCode(int n) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
vector<int> results;

results.push_back(0);
int tmp;
for(int i=0;i<n;i++)
{
for(int j=results.size()-1;j>=0;j--)
{
tmp=results[j]+(1<<i);
results.push_back(tmp);
}
}
return results;
}
};