Leetcode 89. Gray Code

最新推荐文章于 2018-11-17 15:22:33 发布

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本文详细介绍了灰码生成算法的两种实现方式：非递归和递归。通过实例展示了如何使用这两种方法来生成指定位数的灰码序列，并解释了灰码的特点和应用。

Question

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.

Code

非递归

 public List<Integer> grayCode(int n) {
        List<Integer> results = new ArrayList<>();
        results.add(0);
        if (n > 0) {
            results.add(1);
        }
        int mask = 1;
        for (int i = 2; i <= n; i++) {
            mask <<= 1;
            for (int j = results.size() - 1; j >= 0; j--) {
                int t = results.get(j).intValue();
                results.add(t | mask);
            }
        }
        return results;
    }

递归

  public List<Integer> grayCode2(int n) {
        if (n == 0) {
            return Arrays.asList(0);
        }
        List<Integer> results = new ArrayList<>();
        List<Integer> res = grayCode2(n - 1);
        results.addAll(res);
        int mask = 1 << (n - 1);
        for (int j = res.size() - 1; j >= 0; j--) {
            int t = res.get(j).intValue();
            results.add(t | mask);
        }
        return results;
    }