leetCode(13):Remove Duplicates from Sorted List II 分类： leetCode 2015-06-18 16:44 179人阅读 评论(0) 收藏

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.

两种方法

方法一：遍历链表两次，第一次去除重复节点，并把每次删除的结点值保存到容器当中（保存过的值不再保存），第二次遍历，取出容器中的值，并删除链表中相同值的结点；

方法二：一次遍历，指针比较容易出错；

其实，两种方法时间复杂度是一样的，但方法一用到了辅助空间，方法二没有。

方法一：

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
ListNode* deleteDuplicates(ListNode* head)
{
	if(head==NULL)
		return NULL;
	if(head->next==NULL)
		return head;
	vector<int> deleteValue;	
	
	ListNode* p=head;
	int key=p->val;
	p=p->next;
	ListNode* q=head;
	bool flag=false;
	while(p)
	{
		if(p->val==key)
		{
			ListNode* toBeDeleted=p;
			q->next=toBeDeleted->next;
			p=q->next;
			delete toBeDeleted;
			toBeDeleted=NULL;
			if(!flag)
			{
				deleteValue.push_back(key);
				flag=true;
			}
		}
		else
		{
			key=p->val;
			flag=false;
			p=p->next;
			q=q->next;
		}
	}
	p=head;
	q=head;
	vector<int>::iterator iter=deleteValue.begin();
	while(p && iter!=deleteValue.end())
	{
		if(p->val==*iter)
		{
			if(p==head)
			{
				ListNode* toBeDeleted=p;
				p=toBeDeleted->next;
				q=toBeDeleted->next;
				head=q;
				delete toBeDeleted;
				toBeDeleted=NULL;	
			}
			else
			{
				ListNode* toBeDeleted=p;
				q->next=toBeDeleted->next;
				p=q->next;
				delete toBeDeleted;
				toBeDeleted=NULL;	
			}
			iter++;
		}
		else
		{
			if(p!=q)
				q=q->next;				
			p=p->next;
		}
	}
	return head;
}

方法二：

/**
 * 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==NULL)
    		return NULL;
    	if(head->next==NULL)
    		return head;
    	
    	ListNode* p=head;
    	ListNode* q=head;
    	ListNode* k=p->next;
    	
    	bool flag=false;
    	while(k)
    	{
    		if(p->val==k->val)
    		{
    			if(p==q)
    			{
    				p=q=k;
    				head=k;
    				k=k->next;
    			}
    			else
    			{
    				ListNode* toBeDeleted=k;
    				p->next=toBeDeleted->next;
    				k=p->next;
    				delete toBeDeleted;
    				toBeDeleted=NULL;
    			}
    			flag=true;
    		}
    		else
    		{
    			if(flag)
    			{
    				if(p==q)
    				{
    					p=q=k;
    					head=k;
    					k=k->next;
    					flag=false;
    				}
    				else
    				{
    					ListNode* toBeDeleted=p;
    					q->next=toBeDeleted->next;
    					p=k;
    					k=k->next;
    					delete toBeDeleted;
    					toBeDeleted=NULL;
    					flag=false;
    				}
    			}
    			else
    			{
    				if(p!=q)
    					q=q->next;
    				p=p->next;
    				k=k->next;
    			}
    		}		
    	}
    	
    	if(flag)
    	{
    		if(p==q)
    		{
    			delete p;
    			p=NULL;
    			return NULL;
    		}
    		ListNode* toBeDeleted=p;
    		q->next=toBeDeleted->next;
    		delete toBeDeleted;
    		toBeDeleted=NULL;
    	}
    	
    	return head;
    }
};