卖萌的弱渣

I am stupid, I am hungry.

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.

Example

Given n = 2, return [0,1,3,2]. Its gray code sequence is:

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2
3
4

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.

Solution

  • 一部分是n-1位格雷码，再加上 1<<(n-1)和n-1位格雷码的逆序的和。
  • Java
(Gray-Code.java) download
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public class Solution {
        public List<Integer> grayCode(int n) {
            ArrayList<Integer> ret = new ArrayList<Integer>();
            ret.add(0);
            for(int i= 0; i<n; i++){
                int inc = 1 << i;
                for(int j=ret.length()-1; j>=0; j--){
                    ret.add(ret.get(j)+inc);
                }
            }
            return ret;
        }
}
  • Python
(Gray-Code.py) download
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class Solution(object):
    def grayCode(self, n):
        """
        :type n: int
        :rtype: List[int]
        """
        if n == 0:
            return [0]
        # start from n == 0
        seq = self.grayCode(n-1)
        result = seq
        for i in reversed(seq):
            result.append(i | (1<<(n-1)))
        return result