convert binary to decimal using single linked list and recursive method in java

How we can convert binary to decimal using single linked list and recursive method in java? :-s

Ex:

Input: 1->0->0->NULL

Output: 4

I can think of two ways to solve it:

1- If length of list is known:

// To find length of list
public int length(Node head) {
      int count = 0;
      while(head != null) {
         count++;
         head = head.next;
      }
      return count;
   }

public static int convertWhenLengthIsKnown(Node head, int len) {
      int sum = 0;
      if(head.next != null) {
         sum = convertWhenLengthIsKnown(head.next, len-1);
      }
      return sum + head.data * (int)Math.pow(2,len);
   }


   // Call this function as below:

convertWhenLengthIsKnown(head, length(head)-1);

2. If we don't want to calculate length, then we can have a sum variable which is globally accessible,

   private static int sum = 0;
   
   public static int convert(Node head,int i) {
   
     if(head.next != null) {
       i = convert(head.next, i);
     }
     sum += head.data * (int)Math.pow(2,i);
     return i+1;
    }
   
   // Call this function as below:
   
   convert(head,0);
   

Below is the Node class:

class Node {
   int data;
   Node next;

   Node(int data) {
      this.data = data;
   }
}

Hope It helps you.