Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.

Example 1:

Input: 1->2->3->3->4->4->5
Output: 1->2->5

Example 2:

Input: 1->1->1->2->3
Output: 2->3

Answer:

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def deleteDuplicates(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        if head==None:
            return head
        
        newhead=ListNode(head.val-1)
        pnode=newhead
        
        node=head
        
        goodnode=True
        
        while node!=None:
            if node.next==None:
                if goodnode:
                    pnode.next=node
                    pnode=node
                break
            nextnode=node.next
            if node.val!=node.next.val and goodnode:
                pnode.next=node
                pnode=node
                pnode.next=None
                goodnode=True
            elif node.val==node.next.val:
                goodnode=False
            elif not goodnode:
                goodnode=True
            node=nextnode
                
        return newhead.next