Leetcode 线性表 Remove Duplicates from Sorted List II

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Remove Duplicates from Sorted List II

Total Accepted: 10702 Total
Submissions: 43714

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