# [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:
int num2Gray(int num)
{
return num ^ (num >> 1);
}
vector<int> grayCode(int n)
{
vector<int> res ;

int size = 1 << n;// 2^n

for(int i = 0; i < size; i++)
{
res.push_back(num2Gray(i));
}

return res;
}
};

class Solution {
public:
vector<int> grayCode(int n)
{
vector<int> res ;

res.push_back(0);

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

return res;
}
};

posted @ 2015-03-27 14:46  穆穆兔兔  阅读(401)  评论(0编辑  收藏  举报