[轉載]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.

二進制碼->格雷碼（編碼）：從最右邊一位起，依次將每一位與左邊一位異或（XOR），作爲對應格雷碼該位的值，最左邊一位不變（相當於左邊是0）；
格雷碼->二進制碼（解碼）：從左邊第二位起，將每位與左邊一位解碼後的值異或，作爲該位解碼後的值（最左邊一位依然不變）。

Gray Code 0 = 0, 下一項是toggle最右邊的bit(LSB), 再下一項是toggle最右邊值爲 “1” bit的左邊一個bit，然後重複。直到最右邊值爲 “1” 的bit在最左邊了，結束。

class Solution {
public:
    vector<int> grayCode(int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<int> result;
        int nSize = 1 << n;
        for (int i = 0; i < nSize; ++i)
        {
            result.push_back((i>>1)^i);
        }
        return result;
    }
};