leetcode: Merge Two Sorted Lists

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.

/**
* 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) {
// Start typing your C/C++ solution below
// DO NOT write int main() function

ListNode *pl1;
ListNode *pl2;
ListNode *pNewHead;
ListNode *pCur;

if (l1 == NULL && l2 == NULL)
return NULL;

if (l1 == NULL)
return l2;

if (l2 == NULL)
return l1;

pl1 = l1; pl2 = l2;
pNewHead = NULL;

if (pl1->val <= pl2->val)
{
pNewHead = pl1;
pl1 = pl1->next;
}
else
{
pNewHead = pl2;
pl2 = pl2->next;
}

pCur = pNewHead;

while (pl1 && pl2)
{
if (pl1->val <= pl2->val)
{
pCur->next = pl1;
pl1 = pl1->next;
}
else
{
pCur->next = pl2;
pl2 = pl2->next;
}
pCur = pCur->next;
}

if (!pl1)
{
pCur->next = pl2;
}
else
{
pCur->next = pl1;
}

return pNewHead;
}
};