[LeetCode]Remove Linked List Elements

Question

Remove all elements from a linked list of integers that have value val.

Example
Given: 1 –> 2 –> 6 –> 3 –> 4 –> 5 –> 6, val = 6
Return: 1 –> 2 –> 3 –> 4 –> 5

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本题难度Easy。

3指针法

复杂度

时间 O(N) 空间 O(1)

思路

很简单，遇到等于​​val​​的节点就删除，否则就跳过。

代码

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode removeElements(ListNode head, int val) {
        //require
        if(head==null)return head;
        ListNode fake=new ListNode(0);
        fake.next=head;
        ListNode prev=fake,cur=head;
        //invariant
        while(cur!=null){
            ListNode next=cur.next;
            if(cur.val==val){
                prev.next=next;
                cur.next=null;
            }else            
                prev=cur;
            cur=next;
        }
        //ensure
        return fake.next;
    }
}