Java Program to Generate Binary Numbers

In this section, we will create Java programs that generates binary numbers from the specified range (0 to n).

The generation of binary numbers from 1 to n can be achieved through a binary tree. We know that in a tree, every node has two child nodes i.e. right and left nodes. In this binary tree the root node will be 1. In order to get the left and right node of the root node, we will append 0 and 1 respectively at the end of the root node, and so on. Consider the following binary tree for the same.

Let's follow the steps given below to generate the binary numbers.

Create a Queue of type String.
Initialize a variable say n to 0.
Push 1 to the queue, as it is the root node.
While the total is less than n, repeat steps 6 and 7.
Pop the root element from the queue and print it.
Push its left child (element + 0), and the right child (element + 1) to the queue.
Increment the variable total by 1.

Implement the above approach in a Java program.

GenerateBinaryNumbers.java

import java.util.LinkedList;
import java.util.Queue;
public class GenerateBinaryNumbers 
{
private static void generateBinaryNumbers(int n) 
{
if (n == 0) 
{
//returns 0 if n=0    
return;
}
//creating a Queue of type String
Queue<String> que = new LinkedList<>();
//adding the root element to the queue which is the first binary number
que.add("1");
//initialize total as 0
int total = 0;
//check if the total is less than n
while (total < n) 
{
//remove an element from the Queue and print it
String curr = que.poll();
System.out.print(curr + " ");
//appending 0 and 1 in the left and right child respectively 
que.add(curr + "0");
que.add(curr + "1");
//increment the variable total by 1
total++;
}
System.out.println();
}
//main method
public static void main(String args[]) 
{
int n1 = 7;
generateBinaryNumbers(n1);
int n2 = 10;
generateBinaryNumbers(n2);
}
} 

Output:

1 10 11 100 101 110 111 
1 10 11 100 101 110 111 1000 1001 1010

Let's see another logic for the same.

Run a loop from 1 to n. Inside the loop, invoke decimal to binary conversion.

Create an empty Queue of type String.
Add 1 to the queue as the first binary number.
Enqueue the first binary number 1 to the queue.
Run a loop for generating and printing n binary numbers.
1. Dequeue and print the front of the queue.
2. Enqueue the second binary number by appending 0 to the first binary number.
3. Enqueue the third binary number by appending 1 to the first binary number.

The time and space complexity for the following solution is O(n).