面试题---两个有序单链表的合并

#include <iostream>
using namespace std;

struct node{
    int value;
    struct node *next;
};

struct node *head1;
struct node *head2;

void insert(struct node * &head,int value)
{
    if(head == NULL)
    {
        head = new struct node;
        head->value = value;
        head->next = NULL;
        return;
    }

    struct node *p = new struct node;
    p->value = value;
    p->next = NULL;

    struct node *q = head;
    while(q->next != NULL)
    {
        q = q->next;
    }

    q->next = p;

}

struct node *merge(struct node *head1,struct node *head2)
{

    if(head1 == NULL)
        return head2;
    if(head2 == NULL)
        return head1;
    
    struct node *head = NULL;
    if(head1->value > head2->value)
    {
        head = head2;
        head->next = merge(head1,head2->next);
    }
    else
    {
        head = head1;
        head->next = merge(head1->next,head2);
    }
    return head;
}

void print(struct node *head)
{
    struct node *p = head;
    while(p != NULL)
    {
        cout<<p->value<<"  ";
        p = p->next;
    }
}

int main()
{
    head1 = NULL;
    head2 = NULL;

    insert(head1,1);
    if(head1 != NULL)
        cout<<"确实已经赋值了呀！
";
    insert(head1,3);
    insert(head1,5);
    insert(head1,9);
    insert(head1,11);
    insert(head1,16);
    insert(head1,18);
    insert(head2,6);
    insert(head2,10);
    insert(head2,12);
    insert(head2,13);
    insert(head2,15);
    insert(head2,18);
    cout<<"链表1：
";
    print(head1);
    cout<<endl;
    cout<<"链表2：
";
    print(head2);
    cout<<endl;
    cout<<"合并后为
";
    struct node *head = NULL;
    head = merge(head1,head2);
    if(head != NULL)
        print(head);
    cout<<endl;
    return 0;
}