移除链表元素(三种方法)

 

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

 

不使用虚拟头节点:

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

使用虚拟头节点:

/**
 * 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 dummyHead = new ListNode(-1);// 传什么元素无所谓
		dummyHead.next = head;
		ListNode prev = dummyHead;
		while (prev.next != null) {
			if (prev.next.val == val) {
				ListNode delNode = prev.next;
				prev.next = delNode.next;
				delNode.next = null;
			} else {
				prev = prev.next;
			}
		}
		return dummyHead.next;
	}
}

使用递归调用:

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;
	} 
}