You are given the head of a non-empty linked list representing a non-negative integer without leading zeroes.
Return the head of the linked list after doubling it.
Example 1:
Input: head = [1,8,9] Output: [3,7,8] Explanation: The figure above corresponds to the given linked list which represents the number 189. Hence, the returned linked list represents the number 189 * 2 = 378.
Example 2:
Input: head = [9,9,9] Output: [1,9,9,8] Explanation: The figure above corresponds to the given linked list which represents the number 999. Hence, the returned linked list reprersents the number 999 * 2 = 1998.
Constraints:
- The number of nodes in the list is in the range
[1, 104] 0 <= Node.val <= 9- The input is generated such that the list represents a number that does not have leading zeros, except the number
0itself.