【2022初春】【LeetCode】21. 合并两个有序链表

正确返回链表头还是没写对

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        ListNode prehead = new ListNode(0);
        ListNode pre = prehead;
        
        while(l1!=null&&l2!=null){
            if(l1.val<=l2.val){
                pre.next = l1;               
                l1 = l1.next;
            }else{
                pre.next = l2;           
                l2 = l2.next;
            }
            pre = pre.next;
        }
        if(l1!=null) pre.next = l1;
        if(l2!=null) pre.next = l2;
            
        return prehead.next;

    }
}