【leetcode】203. Remove Linked List Elements

203. Remove Linked List Elements

https://leetcode.com/problems/remove-linked-list-elements/?tab=Description

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

思路

用一个新的ListNode fakehead来处理边界情况，fakeHead.next = head;由于本题有可能删除当前节点，所以用双指针pre和curr。

代码

解法一

public class Solution {    public ListNode removeElements(ListNode head, int val) {        ListNode fakeHead = new ListNode(-1);        fakeHead.next = head;        ListNode curr = head, prev = fakeHead;        while (curr != null) {            if (curr.val == val) {                prev.next = curr.next;            } else {                prev = prev.next;            }            curr = curr.next;        }        return fakeHead.next;    }}

解法二 递归

个人不认为这是个好解法，如果LinkedList长度过大，会堆溢出

public ListNode removeElements(ListNode head, int val) {        if (head == null) return null;        head.next = removeElements(head.next, val);        return head.val == val ? head.next : head;}