203. Remove Linked List Elements.md

203. Remove Linked List Elements

Question

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

Example:

Input:  1->2->6->3->4->5->6, val = 6
Output: 1->2->3->4->5

二刷:

• Method 1: 创建一个新的结点，如果符合要求则向这个结点后添加。

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

• Method 2: 原地去除结点，所以要记录前结点。

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode removeElements(ListNode head, int val) {
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode pre = dummy;
        ListNode cur = head;
        while(cur != null){
            while(cur != null && cur.val == val){
                cur = cur.next;
            }
            pre.next = cur;
            if(cur == null) return dummy.next;
            pre = pre.next;
            cur = cur.next;
        }
        return dummy.next;
    }
}