Double-a-Number-represented-as-a-Linked-List.java

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode doubleIt(ListNode head) {
        ListNode tmp = head;
        // Base case
        if(head.val > 4){
            ListNode node = new ListNode(1);
            node.next = head;
            head = node;
        }

        while(tmp != null){
            int carry = 0;
            if(tmp.next != null && tmp.next.val > 4){
                carry = 1;
            }
            int newVal = ((tmp.val * 2) + carry) % 10;
            tmp.val = newVal;
            tmp = tmp.next;
        }
        return head;
    }
}