[LeetCode]Merge Two Sorted Lists

题目描述:(链接)

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.

解题思路：

/**
* 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 *p = &dummy;
while (l1 != nullptr && l2 != nullptr) {
if (l1->val < l2->val) {
p->next = l1;
l1 = l1->next;
} else {
p->next = l2;
l2 = l2->next;
}
p = p->next;
}

if (!l1) {
p->next = l2;
} else {
p->next = l1;
}

return dummy.next;
}
};