LeetCode 21 链表 Merge Two Sorted Lists

LeetCode 21 链表 Merge Two Sorted Lists

LeetCode

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

Example:

Input: 1->2->4, 1->3->4
Output: 1->1->2->3->4->4

代码：
递归

class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {        
        if(l1 == null) return l2;
        if(l2 == null) return l1;
        if(l1.val < l2.val){
            l1.next = mergeTwoLists(l1.next, l2);
            return l1;
        }else{
            l2.next = mergeTwoLists(l1, l2.next);
            return l2;
        }
    }    
}

迭代

class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {        
        ListNode head = new ListNode(0);
        ListNode cur = head;
        while(l1 != null && l2 != null){
            if(l1.val <l2.val){
                cur.next = l1;
                l1 = l1.next;
            }else{
                cur.next = l2;
                l2 = l2.next;
            }
            cur = cur.next;
        }
        if(l1 != null){
            cur.next = l1;
        }
        if(l2 != null){
            cur.next = l2;
        }
        return head.next;
    }    
}

注意：