_89.java

package com.fishercoder.solutions;

import com.fishercoder.common.utils.CommonUtils;

import java.util.ArrayList;
import java.util.List;

/**
 * 89. 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,
 * 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.
 */

public class _89 {

    public List<Integer> grayCode(int n) {
        List<Integer> result = new ArrayList();
        for (int i = 0; i < (1 << n); i++) {
            result.add(i ^ (i >> 1));
        }
        return result;
    }

    public static void main(String... args) {
        int n = 3;
        System.out.println("1 << n = " + (1 << n));
        _89 test = new _89();
        List<Integer> result = test.grayCode(n);
        CommonUtils.printList(result);
    }
}