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

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.

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

storeList.push_back(0);
retVector.push_back(0);

if (n == 0)
return retVector;

storeList.push_back(1);
retVector.push_back(1);

if (n == 1)
{
return retVector;
}

for (int i = 2; i <= n; i++)
{

list<int>::iterator itr = storeList.end();
int snapshotSize = storeList.size();
int curAddNum = 1 << (i-1);

for (int j = snapshotSize; j > 0; j--)
{
--itr;
int curNum = (*itr) + curAddNum;
storeList.push_back(curNum);
retVector.push_back(curNum);
}

}

return retVector;

}
};