83. Remove Duplicates from Sorted List （easy）

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

遍歷一遍，如果pre和cur的val相同，就把pre指向cur.next，如果不同 就pre和cur都往後移動一個 

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

class Solution:
    def deleteDuplicates(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        if not head:return []
        pre = head
        cur = pre.next
        while(cur):
            
            if cur.val == pre.val:
                cur = cur.next
                pre.next = cur
            else:
                pre = cur
                cur = cur.next
                
        return head
        
 

或者只用一個cur指標

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

class Solution:
    def deleteDuplicates(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        if not head:return []
        cur = head
        while(cur.next):
            if cur.val == cur.next.val:
                cur.next = cur.next.next
            else:cur = cur.next
                
        return head