【leetcode】203. Remove Linked List Elements

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

key:需要移除所有等於val的結點!

題解如下：

1.利用遞歸

/**
 * 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) {
        if(head == null)
            return null;
        head.next = removeElements(head.next,val);
        return head.val == val? head.next:head;
    }
}

2.非遞歸版本

/**
 * 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) {
        while(head != null && head.val == val)
            head = head.next;
        ListNode cur = head;
        while(cur != null && cur.next != null) {
            if(cur.next.val == val)
                cur.next = cur.next.next;
            else
                cur = cur.next;
        }
        return head;
    }
}