203.移除链表元素

题目描述

删除链表中等于给定值 val 的所有节点。

示例:

输入: 1->2->6->3->4->5->6, val = 6
输出: 1->2->3->4->5

 

注意点

1、删除点在开头；

2、删除点在结尾；

3、连续删除两个位置；

4、需delete手动释放内存；

 

头结点命中处理

1、头结点命中特殊处理；

 

 

 

2、引入虚拟头结点；

 

 

 

删除操作

1、两个指针完成删除；

 

 

 

2、一个指针完成删除；

 

 

 

方法一

头结点命中特殊处理，利用两个指针完成删除操作；

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/**  * Definition for singly-linked list.  * struct ListNode {  *     int val;  *     ListNode *next;  *     ListNode(int x) : val(x), next(NULL) {}  * };  */ class Solution { public:     ListNode* removeElements(ListNode* head, int val) {         if( head == NULL )             return head;           ListNode *p = head;         ListNode *pre = p;         while( p )         {             if( p->val == val )             {                 if( pre == p )                 {                     head = head->next;                     p = head;                     pre = p;                 }                 else                 {                     pre->next = p->next;                     p = p->next;                 }             }             else             {                 pre = p;                 p = p->next;             }         }           return head;     } };

　　

　

方法二

引入虚拟头结点，利用两个指针完成删除操作；

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/**  * Definition for singly-linked list.  * struct ListNode {  *     int val;  *     ListNode *next;  *     ListNode(int x) : val(x), next(NULL) {}  * };  */ class Solution { public:     ListNode* removeElements(ListNode* head, int val) {         if( head == NULL )             return head;           ListNode *res = new ListNode(0);         ListNode *p = head;         res->next = head;         ListNode *pre = res;         while( p )         {             if( p->val == val )                 pre->next = p->next;             else                 pre = p;             p = p->next;         }           return res->next;     } };

　　

方法三

引入虚拟头结点，一个指针完成删除；

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/**  * Definition for singly-linked list.  * struct ListNode {  *     int val;  *     ListNode *next;  *     ListNode(int x) : val(x), next(NULL) {}  * };  */ class Solution { public:     ListNode* removeElements(ListNode* head, int val) {         if( head == NULL )             return head;           ListNode *res = new ListNode(0);         res->next = head;         ListNode *p = res;           while( p->next )         {             if( p->next->val == val )             {                 ListNode *tmp = p->next;                 p->next = p->next->next;                 delete tmp;             }             else                 p = p->next;         }           return res->next;     } };