LeetCode 21 Merge Two Sorted Lists

// Author : yqtao
// Date   : 2016-7-3
// Email  : yqtao@whu.edu.cn
/**********************************************************************************
*
* 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) {}
* };
*/

ListNode *mergeTwoLists(ListNode *l1, ListNode *l2) {
ListNode dummy(INT_MIN);
ListNode *tail = &dummy;

while (l1 && l2) {
if (l1->val < l2->val) {
tail->next = l1;
l1 = l1->next;
}
else {
tail->next = l2;
l2 = l2->next;
}
tail = tail->next;
}

tail->next = l1 ? l1 : l2;
return dummy.next;
}