remove duplicates from sorted list.py

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

class Solution:
    # @param head, a ListNode
    # @return a ListNode
    def deleteDuplicates(self, head):
        if not head:
            return None
            
        p1 = head;
        p2 = head.next;
        while p2:
            if p1.val == p2.val:
                p2 = p2.next
                p1.next = p2
            else:
                p1 = p1.next;
                p2 = p2.next;
                
        return head