This is my CPP solution.
class Solution {
public:
ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
ListNode *dummy = new ListNode(0);
ListNode *head = dummy;
while(l1!=NULL && l2!=NULL){
if(l1->val <= l2->val){
dummy->next = l1;
l1 = l1->next;
}
else{
dummy->next = l2;
l2 = l2->next;
}
dummy = dummy->next;
}
if(l1!=NULL){
dummy->next = l1;
}
else{
dummy->next = l2;
}
return head->next;
}
};