LeetCode (Merge Two Sorted Lists)

Problem:

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.

Solution:

/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
ListNode l(0), *p = &l;
while(p != NULL){
if(l1 != NULL && l2 != NULL){
if(l1->val < l2->val){
p->next = l1;
l1 = l1->next;
}
else{
p->next = l2;
l2 = l2->next;
}
p = p->next;
}
else if(l1 == NULL){
p->next = l2;
break;
}
else{
p->next = l1;
break;
}
}
return l.next;
}
};