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Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.
For example,
Given 1->2->3->3->4->4->5, return 1->2->5.
Given 1->1->1->2->3, return 2->3.
题意：将已排序的链表中所有重复的元素移除
思路：
三个个指针，pre, cur, next
一个布尔变量is_appear，表示cur指针指向的值之前是否已经出现过
检查cur, next指向的节点的值是否相同，
相同的话，删除cur
不同的话，如果is_appear为true，删除cur，否则不删除
删除的话，只移动cur, next指针
不删除的话，要移动pre, cur, next三个指针
复杂度：时间O(n)，空间O(1)
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode *deleteDuplicates(ListNode *head) {
if(!head || !head->next) return head;
ListNode tem(0);
ListNode *dummy = &tem;
dummy->next = head;
ListNode *pre = dummy, *cur = head, *next = head->next;
bool is_appear = false;
while(cur && next){
if(cur->val == next->val || is_appear){
is_appear = cur->val == next->val;
pre->next = next;
delete cur;
cur = next;
next =next->next;
}else{
pre = cur;
cur = next;
next = next->next;
is_appear = false;
}
}
if(is_appear){
pre->next = NULL;
delete cur;
}
return dummy->next;
}
};Leetcode 线性表 Remove Duplicates from Sorted List II,布布扣,bubuko.com
Leetcode 线性表 Remove Duplicates from Sorted List II
原文：http://blog.csdn.net/zhengsenlie/article/details/25781315