Difficulty: Medium
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].
Language: Java
class Solution {
public List<Integer> grayCode(int n) {
List<Integer> result = new ArrayList<>();
result.add(0);
for (int i = 0; i < n; i++) {
for (int j = result.size() - 1; j >= 0; j--) { // 从尾部开始，用于保持连续（即每次只差一个bit位）
result.add(result.get(j) | 1 << i);
}
}
return result;
}
}