合并两个排序的链表

Posted 2020-10-18 Jeysin

题目描述

　　输入两个单调递增的链表，输出两个链表合成后的链表，当然我们需要合成后的链表满足单调不减规则

　　解法1：非递归解法

 1 class Solution {
 2 public:
 3     ListNode* Merge(ListNode* pHead1, ListNode* pHead2)
 4     {
 5         if(!pHead1 && !pHead2)return NULL;
 6         if(pHead1 && !pHead2)return pHead1;
 7         if(!pHead1 && pHead2)return pHead2;
 8         ListNode *newHead;
 9         if(pHead1->val < pHead2->val)
10         {
11             newHead=pHead1;
12             pHead1=pHead1->next;
13         }else{
14             newHead=pHead2;
15             pHead2=pHead2->next;
16         }
17         ListNode *tmp=newHead;
18         while(pHead1 && pHead2)
19         {
20             if(pHead1->val < pHead2->val)
21             {
22                 tmp->next=pHead1;
23                 tmp=tmp->next;
24                 pHead1=pHead1->next;
25             }else{
26                 tmp->next=pHead2;
27                 tmp=tmp->next;
28                 pHead2=pHead2->next;
29             }
30         }
31         if(pHead1)tmp->next=pHead1;
32         if(pHead2)tmp->next=pHead2;
33         return newHead;
34     }
35 };

 

　　解法2：递归解法

 1 class Solution {
 2 public:
 3     ListNode* Merge(ListNode* pHead1, ListNode* pHead2)
 4     {
 5         if(pHead1==NULL)return pHead2;
 6         if(pHead2==NULL)return pHead1;
 7         ListNode *newHead;
 8         if(pHead1->val < pHead2->val)
 9         {
10             newHead=pHead1;
11             newHead->next=Merge(pHead1->next, pHead2);
12         }else{
13             newHead=pHead2;
14             newHead->next=Merge(pHead1, pHead2->next);
15         }
16         return newHead;
17     }
18 };