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：
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
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].
解释下题目：
在一组数的编码中，若任意两个相邻的代码只有一位二进制数不同，则称这种编码为格雷码。生成格雷码。我记得通信概论里面还学过这个。。
1. 发现规律做
实际耗时：1ms
public List<Integer> grayCode(int n) {
List<Integer> res = new ArrayList<>();
if (n < 0) {
return res;
} else if (n == 0) {
res.add(0);
return res;
} else if (n == 1) {
res.add(0);
res.add(1);
return res;
} else {
res.add(0);
res.add(1);
for (int i = 1; i < n; i++) {
int tmp = (int) Math.pow(2, i);
for (int j = tmp - 1; j >= 0; j--) {
res.add(res.get(j) + tmp);
}
}
return res;
}
}
思路就是自己画个格雷码找规律就行了。而且规律还不止一种
