[leetcode] 21. Merge Two Sorted Lists

题目链接：https://leetcode.com/problems/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.

思路

建立一个虚头结点, 然后每次取两个结点中比较小的即可.

/**
* 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* pHead = new ListNode(0),*p = pHead,*q;
while(l1 || l2){
if(!l2 || (l1 && l1->val < l2->val)){
q = l1;
l1 = l1->next;
}
else{
q = l2;
l2 = l2->next;
}
p->next = q;
p = p->next;
}
p->next = NULL;
p = pHead->next;
delete pHead;
return p;
}
};