[leetcode 21] 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) {
if (!l1) {
return l2;
}
if (!l2) {
return l1;
}
ListNode dummy(-1);
ListNode *cur = &dummy;
for ( ; l1 && l2; cur = cur->next) {
if (l1->val > l2->val) {
cur->next = l2;
l2 = l2->next;
} else {
cur->next = l1;
l1 = l1->next;
}
}
cur->next = l1 != NULL?l1:l2;
return dummy.next;
}
};