递归版:
ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
if(!l1) return l2;
else if(!l2) return l1;
ListNode* res = nullptr;
if(l1->val < l2->val)
{
res = l1;
res->next = mergeTwoLists(l1->next, l2);
}
else
{
res = l2;
res->next = mergeTwoLists(l1, l2->next);
}
return res;
}
非递归版:
ListNode* mergeTwoLists(ListNode* l1, ListNode* l2)
{
if (l1 == nullptr)
return l2;
if (l2 == nullptr)
return l1;
ListNode* p = new ListNode(-100);
ListNode* res = p;
while (l1 && l2)
{
if (l1->val < l2->val)
{
p->next = l1;
l1 = l1->next;
}
else
{
p->next = l2;
l2 = l2->next;
}
p = p->next;
}
p->next = l1 ? l1 : l2;
return res->next;
}