Given a sorted linked list, delete all duplicates such that each element appear only once.

Example 1:

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

Example 2:

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

LeetCode：連結

這題和82不一樣的是，不需要考慮之前的節點，因為要保留一個值。

# 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 not head:
            return None
        phead = head
        while phead:
            if phead.next and phead.val == phead.next.val:
                pnext = phead.next
                while pnext.next and pnext.next.val == phead.val:
                    pnext = pnext.next
                phead.next = pnext.next                
                phead = pnext.next
            else:
                phead = phead.next
        return head