leetcode83 Remove Duplicates from Sorted List

"""
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
"""
"""
删除链表结点，操作这类的题，一般需要定义两个指针
分别指向head 和 head.next 然后画图总结规律
"""
class ListNode:
    def __init__(self, x):
        self.val = x
        self.next = None

class Solution:
    def deleteDuplicates(self, head):
        if head == None:
            return head
        p = head
        q = head.next
        while q:
            if p.val == q.val:
                p.next = q.next
                q = p.next
            else:
                p = p.next
                q = q.next
        return head