leetcode - 89.Gray Code

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.

For now, the judge is able to judge based on one instance of gray code sequence. Sorry about that.

Solution1:

public List<Integer> grayCode(int n) {
List<Integer> result = new ArrayList<>();
result.add(0);
for (int i = 0; i < n; i++) {
int size = result.size();
for (int k = size - 1; k >= 0; k--)
result.add(result.get(k) | 1 << i);
}
return result;
}

Solution2:

better

public List<Integer> grayCode(int n) {
List<Integer> result = new ArrayList<>();
for (int i = 0; i < 1 << n; i++)
result.add(i ^ i >> 1);
return result;
}