迭代
class Solution {
public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
ListNode dummy = new ListNode(), h = dummy;
while(l1 != null && l2 != null){
if(l1.val < l2.val){
h.next = l1;
l1 = l1.next;
}else{
h.next = l2;
l2 = l2.next;
}
h = h.next;
}
h.next = l1 != null ? l1 : l2;
return dummy.next;
}
}
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;
}
}
}