Swap First and Last Digit

/*
 * Problem : Swap the first and the last digit.
 * Input   : One positive integer.
 * Output  : The new number.
 * Approach: Use arithmetic: first = n / 10^(d-1), last = n % 10.
 * Time    : O(d)
 * Space   : O(1)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        long number = new Scanner(System.in).nextLong();

        // Step 1: A number with one digit does not change.
        if (number < 10) {
            System.out.println(number);
            return;
        }

        // Step 2: Find the place value of the first digit. Example: 1234 -> 1000.
        long power = 1;
        while (number / power >= 10) {
            power = power * 10;
        }

        // Step 3: Take the first digit and the last digit. Example: 1234 -> first = 1, last = 4.
        long first = number / power;
        long last = number % 10;

        // Step 4: Take the middle digits. Remove the first digit and the last digit. Example: 1234 -> 23.
        long middle = (number % power) / 10;

        // Step 5: Build the result: last digit, then middle digits, then first digit. Example: 4 * 1000 + 23 * 10 + 1 = 4231.
        long result = last * power + middle * 10 + first;

        // Step 6: Print the result.
        System.out.println(result);
    }
}