lintcode-medium-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, find the sequence of gray code. A gray code sequence must begin with

0

and with cover all 2n integers.

Given

n = 2

, return

[0,1,3,2]

. Its gray code sequence is:

00 - 0
01 - 1
11 - 3
10 - 2

[/code]

public class Solution {
/**
* @param n a number
* @return Gray code
*/
public ArrayList<Integer> grayCode(int n) {
// Write your code here
ArrayList<Integer> result = new ArrayList<Integer>();

if(n < 0)
return result;

if(n == 0){
result.add(0);
return result;
}

result.add(0);
result.add(1);

for(int i = 2; i <= n; i++){
ArrayList<Integer> new_half = new ArrayList<Integer>();
for(int j = result.size() - 1; j >= 0; j--)
new_half.add(result.get(j) + (1 << (i - 1)));

result.addAll(new_half);
}

return result;
}
}