合并两个排序的链表(递归&非递归)

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。

（1）递归版本

/* struct ListNode { int val; struct ListNode *next; ListNode(int x) : val(x), next(NULL) { } };*/

class Solution 
{
public:
    ListNode* Merge(ListNode* pHead1, ListNode* pHead2)
    {
        
       
       if(nullptr == pHead1) 
           return pHead2;
          if(nullptr == pHead2) 
           return pHead1;
        if(pHead1->val > pHead2->val)
        {
            pHead2->next = Merge(pHead1,pHead2->next);
            return pHead2;
        }
        else
        {
            pHead1->next = Merge(pHead1->next,pHead2);
            return pHead1;
        }
        
    }
};

（2）非递归版本

/* struct ListNode { int val; struct ListNode *next; ListNode(int x) : val(x), next(NULL) { } };*/

class Solution 
{
public:
    ListNode* Merge(ListNode* pHead1, ListNode* pHead2)
    {
        
        //非递归
        if(nullptr == pHead1 && nullptr == pHead2)
            return nullptr;
        ListNode * pHead = new ListNode(0);
        ListNode * cur = pHead ;
        while(true)
        {
            if(nullptr == pHead1)
            {
                cur->next =pHead2;
                break;
            }
            else if(nullptr == pHead2)
            {
                cur->next = pHead1;
                break; 
            }
             if(pHead1->val > pHead2->val)
                swap(pHead1, pHead2);
            cur->next = pHead1;
            cur = cur->next;
            pHead1 = pHead1->next;
    }
         return pHead->next;
    }
};

<stron>：合并两个排序的链表</stron>