【Leetcode】Gray Code (Pascal)

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.

八字口诀就可以把这道题解决

左移加数，倒序相加

意思是把1左移0~n-1位然后和原数组记录的所有数倒序相加就能得到结果了

public static ArrayList<Integer> grayCode(int n) {
ArrayList<Integer> result = new ArrayList<Integer>();
result.add(0);

for (int i = 0; i < n; i++) {
int inc = 1 << i;
for (int j = result.size() - 1; j >= 0; j--) {
result.add(result.get(j) + inc);
}
}
return result;
}