LeetCode Online Judge 题目C# 练习 - 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

Gray Code， 每次看每次都不记得。写下来让自己好温习。

Gray Code 0 = 0, 下一项是toggle最右边的bit(LSB), 再下一项是toggle最右边值为 “1” bit的左边一个bit。然后重复

如： 3bit

Gray Code: 000, 001, 011, 010, 110, 111, 101, 100, 最右边值为 “1” 的bit在最左边了，结束。

Binary : 000, 001, 010, 011, 100, 101, 110, 111

再者就是Binary Code 转换为Gray Code了。

如：

　　Binary Code ：1011 要转换成Gray Code

　　1011 = 1（照写第一位）, 1(第一位与第二位异或 1^0 = 1), 1(第二位异或第三位， 0^1=1), 0 (1^1 =0) = 1110

　　其实就等于 (1011 >> 1) ^ 1011 = 1110

有了上面的等式写code就简单了

public static List<int> GrayCode(int n)
{
List<int> ret = new List<int>();

int size = 1;
while (n-- > 0) size *= 2; //calculate how many number would be. 2^n

for (int i = 0; i < size; i++)
{
ret.Add((i >> 1) ^ i);
}

return ret;
}