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.

Example 1:

Input: 2
Output: [0,1,3,2]
Explanation:
00 - 0
01 - 1
11 - 3
10 - 2
For a given n, a gray code sequence may not be uniquely defined.
For example, [0,2,3,1] is also a valid gray code sequence.
00 - 0
10 - 2
11 - 3
01 - 1

Example 2:

Input: 0
Output: [0]
Explanation: We define the gray code sequence to begin with 0.
A gray code sequence of n has size = 2n, which for n = 0 the size is 20 = 1.
Therefore, for n = 0 the gray code sequence is [0].

AC代码

class Solution {
public:
    vector<int> grayCode(int n) {
        int size = pow(2, n);
        vector<int> res(size);
        for (int i = 0; i < n; ++i) {
            int base = pow(2, i);
            for (int j = base, k = 1; j < pow(2, i + 1); j++, k += 2) 
                res[j] = base + res[j - k];            
        }
        return res;
    }
};

总结

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