leetcode21 合并两个排好序的单链表

/**
* 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* p1=l1;
ListNode* p2=l2;
if(l1==NULL){
return l2;
}
else if(l2==NULL){
return l1;
}
ListNode* cur=(l1->val<=l2->val?l1:l2);
ListNode* head=cur;
if(l1->val<=l2->val){
p1=p1->next;
}
else{
p2=p2->next;
}
while(p1&&p2){
if(p1->val<=p2->val){
cur->next=p1;
p1=p1->next;
}
else{
cur->next=p2;
p2=p2->next;
}
cur=cur->next;
}
while (p1){
cur->next = p1;
p1 = p1->next;
cur = cur->next;
}
while (p2){
cur->next = p2;
p2 = p2->next;
cur = cur->next;
}
return head;
}
};

<pre name="code" class="cpp">ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
if (l1 == NULL) return l2;
if (l2 == NULL) return l1;
if (l1->val <= l2->val) {
l1->next = mergeTwoLists(l1->next, l2);
return l1;
} else {
l2->next = mergeTwoLists(l1, l2->next);
return l2;
}
}