c++ 如何合并两个有序链表

#include <sstream>
#include <iostream>
using namespace std;

struct ListNode 
{ 
  int     value; 
  ListNode*  next;
  ListNode() {value=0;next=NULL;}
  ListNode(int value,ListNode* next = NULL):value(value),next(next){} 
};

//@brief:非递归实现两个有序单链表
//@注意：两个链表需要从小到大顺序排列
ListNode* mergeOrderedLinkedList(ListNode* head1,ListNode* head2)
{
  if (head1 == NULL) 
  { 
    return head2; 
  }
  else if(head2 == NULL) 
  { 
    return head1; 
  }

  ListNode* mergeHead = NULL; 
  if (head1->value<head2->value) 
  { 
    mergeHead=head1;
    head1=head1->next;
  } 
  else 
  { 
    mergeHead = head2; 
    head2 = head2->next; 
  } 
  ListNode* tmpNode = mergeHead; 
  while(head1&&head2)
  { 
    if(head1->value<head2->value) 
    { 
      mergeHead->next = head1; 
      head1 = head1->next; 
    } 
    else 
    { 
      mergeHead->next = head2; 
      head2 = head2->next; 
    } 
    mergeHead = mergeHead->next; 
  } 
  if (head1)
  { 
    mergeHead->next = head1; 
  } 
  if (head2) 
  { 
    mergeHead->next = head2; 
  }

  return tmpNode; 
}

//打印链表
void printLinkedList(ListNode* head)
{
  while(head)
  {
    cout<<head->value<<" ";
    head=head->next;
  }
  cout<<endl;
}

int main(int argc,char* argv[])
{
  ListNode* head1=NULL,*curList1=NULL,*head2=NULL,*curList2=NULL;
  string strIn;
  int value;

  cout<<"创建链表1，从小到大顺序输入链表1："<<endl;
  getline(cin,strIn);
  stringstream ss(strIn);
  cout<<"ss0 strIn:"<<ss.str()<<endl;
  while(ss>>value)    //从string中按照空格读取int
  {
    ListNode* newNode1=new ListNode;
    newNode1->value=value;
    if(head1==NULL && curList1==NULL)
    {
      head1=newNode1;
      curList1=newNode1;
    }
    else
    {
      curList1->next=newNode1;
      curList1=curList1->next;
    }
  }

  cout<<"创建链表2，从小到大顺序输入链表2："<<endl;
  getline(cin,strIn);
  ss.clear(); //清空状态
  ss.str(""); //清空内容
  ss<<strIn;  //重新输出至string
  cout<<"ss1 strIn:"<<ss.str()<<endl;
  while(ss>>value)    //从string中按照空格读取int
  {
    ListNode* newNode2=new ListNode;
    newNode2->value=value;
    if(head2==NULL && curList2==NULL)
    {
      head2=newNode2;
      curList2=newNode2;
    }
    else
    {
      curList2->next=newNode2;
      curList2=curList2->next;
    }
  }

  //合并两个有序链表
  ListNode* mergeHead=mergeOrderedLinkedList(head1,head2);

  //打印链表
  cout<<"合并后链表："<<endl;
  printLinkedList(mergeHead);
}

//@brief:递归实现两个有序单链表
//@注意：两个链表需要从小到大顺序排列
ListNode* mergeOrderedLinkedListRecursion(ListNode* head1,ListNode* head2)
{
  if(head1 == NULL) 
  { 
    return head2; 
  }
  else if(head2 == NULL) 
  { 
    return head1; 
  }

  ListNode* mergeHead = NULL;
  if(head1->value<head2->value) 
  {
    mergeHead=head1;
    mergeHead->next=mergeOrderedLinkedListRecursion(head1->next,head2);
  }
  else
  {
    mergeHead=head2;
    mergeHead->next=mergeOrderedLinkedListRecursion(head1,head2->next);
  }
  return mergeHead;
}