力扣第203号问题的三种解法

Posted 2022-04-29 *平芜尽处是春山*

203、移除链表元素

解法一

class Solution 
    public ListNode removeElements(ListNode head, int val) 
        while(head != null && head.val == val) 
            ListNode node = head;
            head = head.next;
            node.next = null;
        
        if(head == null) 
            return null;
         else 
            ListNode prev = head;
            while(prev.next != null) 
                if(prev.next.val == val) 
                    ListNode node = prev.next;
                    prev.next = node.next;
                    node.next = null;
                 else 
                    prev = prev.next;
                
            
            return head;
        
    

运行截图：

解法二（虚拟头结点）

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

运行截图：

解法三（递归）

class Solution 
    public ListNode removeElements(ListNode head, int val) 
     if(head == null) 
            return null;
        
        head.next = removeElements(head.next,val);
        if(head.val == val) 
            return head.next;
        
        return head;
    

简化：

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;
    

运行截图：