_89.java

package com.fishercoder.solutions;

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

public class _89 {

    public static class Solution1 {
        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 class Solution2 {
        public List<Integer> grayCode(int n) {
            List<Integer> result = new ArrayList();
            for (int i = 0; i < Math.pow(2, n); i++) {
                result.add(i ^ (i >> 1));
            }
            return result;
        }
    }

    public static void main(String... args) {
        System.out.println("-----------------------------------------------------------------------------------------");
        System.out.println("How to understand i << n? It means n to the power of two, see below. So we have an equivalent solution, which is solution2.");
        System.out.println("1 << 2: " + (1 << 2));
        System.out.println("1 << 3: " + (1 << 3));
        System.out.println("1 << 4: " + (1 << 4));
        System.out.println("1 << 5: " + (1 << 5));
        System.out.println("1 << 6: " + (1 << 6));
        System.out.println("-----------------------------------------------------------------------------------------");
        System.out.println("How to understand i >> 1? It means to shift the number i to the right by 1 bit, see below");
        System.out.println("0 >> 1: " + (0 >> 1));
        System.out.println("1 >> 1: " + (1 >> 1));
        System.out.println("2 >> 1: " + (2 >> 1));
        System.out.println("3 >> 1: " + (3 >> 1));
        System.out.println("4 >> 1: " + (4 >> 1));
        System.out.println("5 >> 1: " + (5 >> 1));
        System.out.println("6 >> 1: " + (6 >> 1));
    }

}