Plus One Linked List

Description:

Given a non-negative integer represented as non-empty a singly linked list of digits, plus one to the integer.

You may assume the integer do not contain any leading zero, except the number 0 itself.

The digits are stored such that the most significant digit is at the head of the list.

Example Given head = 1 -> 2 -> 3 -> null, return 1 -> 2 -> 4 -> null.

Code:

"""
Definition of ListNode
class ListNode(object):
    def __init__(self, val, next=None):
        self.val = val
        self.next = next
"""

class Solution:
    """
    @param head: the first Node
    @return: the answer after plus one
    """
 

    def plusOne(self, head):
        # Write your code here
        def dfs(node):
            if not node.next or dfs(node.next):
                (node.val, add) = (node.val+1, False) if node.val<9 else (0, True)
                return add
        return head if not dfs(head) else ListNode(1, head)