[leetcode] Gray Code

he 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 - 001 - 111 - 310 - 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() functionvector<int> ret;if(n>32)return ret;set<int> checked;ret.push_back(0);checked.insert(0);unsigned int num=0;unsigned int flag=1;unsigned int direction=0;bool nonum=true;int i=0;for( ; ; direction=!direction,nonum=true){for(i=0 ; i<n ; i++){if(direction && i!=0)flag>>=1;if(!direction && i!=0)flag<<=1;if(checked.count(num^flag))continue;else{num^=flag;ret.push_back(num);checked.insert(num);nonum=false;}}if(nonum==true && i==n)break;}return ret;}};

格雷码的问题，给出一个更一般的解：

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

简单明了