【Leetcode】：89. Gray Code 问题 in JAVA

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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 10-2 11-3

这道题目要求计算格雷码，输出对应的十进制数字，难度为中等，不过实现起来还是很简单的。

public class Solution {    public List<Integer> grayCode(int n) {        if (n == 0) {            List<Integer> list = new ArrayList<Integer>();            list.add(0);            return list;        }        if (n == 1) {            List<Integer> list = new ArrayList<Integer>();            list.add(0);            list.add(1);            return list;        }        List<Integer> grayM = grayCode(n - 1);        List<Integer> list = new ArrayList<Integer>();        for (int i = 0; i < Math.pow(2,n); i++) {            if (i < Math.pow(2, n-1)) { //前面一半的数字不变                list.add(grayM.get(i));                } else { //后面一半的数字反向排列，再在前面添加一个‘1’                int res =  grayM.get( (int)Math.pow(2, n) - i - 1 ) + (int)Math.pow(2, n - 1);                list.add(res);              }        }        return list;    }}

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