🔗 Reversing a Natural Number into an Array

Reverse the natural number n and return it as an array containing each digit as an element. For example, if n is 12345, return [5,4,3,2,1].

• n is a natural number no greater than 10,000,000,000.

Reverse the natural number n and return each digit as an array.

There is also a method of converting the number into a string and arranging each character in reverse order. But this time, let's solve it using numeric operations.

Declare an ArrayList to hold each digit.

JAVA
ArrayList<Integer> list = new ArrayList<>();

while (n >= 10)
{
	list.add((int) (n % 10));
	
	n /= 10;
}

list.add((int) n);

You can get the last digit with n % 10, and get the remaining number excluding that digit with n / 10. Repeat this operation until n becomes smaller than 10.

Since we obtain the digits starting from the ones place, we don't even need to reverse the array — we can just return it as it is.

JAVA
import java.util.ArrayList;

/**
 * Reversing a Natural Number into an Array class
 *
 * @author RWB
 * @since 2021.12.13 Mon 18:31:27
 */
class Solution
{
	/**
	 * Method that returns the answer
	 *
	 * @param n: [long] natural number
	 *
	 * @return [int[]] answer
	 */
	public int[] solution(long n)
	{
		ArrayList<Integer> list = new ArrayList<>();
		
		while (n >= 10)
		{
			list.add((int) (n % 10));
			
			n /= 10;
		}
		
		list.add((int) n);
		
		return list.stream().mapToInt(Integer::intValue).toArray();
	}
}