Form a number using corner digits of powers

// Java program to find number formed by
// corner digits of powers.
import java.io.*;
import java.util.*;
 
public class GFG {
    
    static List<Integer> power = new ArrayList<Integer>();
    // Find next power by multiplying N 
    // with current power
    static void nextPower(Integer N)
    {
        Integer carry = 0;
     
        for (int i = 0; i < power.size(); i++)
        {
            Integer prod = (power.get(i) * N) + carry ;
     
            // Store digits of Power one by one.
            power.set(i,prod % 10);
     
            // Calculate carry.
            carry = prod / 10 ;
        }
     
        while (carry >= 1)
        {
            // Store carry in Power array.
            power.add(carry % 10);
            carry = carry / 10 ;
        }
    }
     
    // Prints number formed by corner digits of
    // powers of N.
    static void printPowerNumber(int X, int N)
    {
         
        // Storing N raised to power 0
        power.add(1);
     
        // Initializing empty result
        List<Integer> res = new ArrayList<Integer>();
     
        // One by one compute next powers and
        // add their corner digits.
        for (int i = 1; i <= X; i++)
        {
            // Call Function that store power
            // in Power array.
            nextPower(N) ;
     
            // Store unit and last digits of
            // power in res.
            res.add(power.get(power.size() - 1));
            res.add(power.get(0));
        }
     
        for (int i = 0 ; i < res.size(); i++)
            System.out.print(res.get(i)) ;
    }
     
    // Driver Code
    public static void main(String args[])
    {
        Integer N = 19 , X = 4;
        printPowerNumber(X, N);
    }
}
 
// This code is contributed by Manish Shaw
// (manishshaw1)