Generate n-bit gray codes. Given a number n, generate bit patterns from 0 to 2^n-1 such that successive patterns differ by one bit.

nBitGrayCode.java

import java.io.*;
import java.lang.*;
import java.util.*;

class nBitGrayCode {

    public static void main(String[] args) {
    
        int n = 3;
        
        ArrayList<StringBuilder> list = new ArrayList<>();
        list.add(new StringBuilder("0"));
        list.add(new StringBuilder("1"));

        ArrayList<StringBuilder> list1 = new ArrayList<>();
        ArrayList<StringBuilder> list2 = new ArrayList<>();

        for (StringBuilder s : list) {
            list1.add(new StringBuilder(s));
            list2.add(new StringBuilder(s));
        }

        for (int i = 0; i < n-1; i++) {
            
            for (StringBuilder a : list1)
                a.insert(0, "0");

            // System.out.println(list1);

            for (StringBuilder b : list2)
                b.insert(0, "1");

            // System.out.println(list2);

            list.clear();
            list.addAll(list1);
            list.addAll(list2);

            list1.clear();
            for (StringBuilder s : list) {
                list1.add(new StringBuilder(s));
            }

            list2.clear();
            for (StringBuilder s : list) {
                list2.add(new StringBuilder(s));
            }

            System.out.println(list + "\n");

        }

    }

}