单链表归并排序

#include <iostream>  
#include <stack>  
#include <vector>  
#include <deque> 
using namespace std;


typedef struct student{
	int num;
	int score;
	student *next;
}student;

//创建一个单向链表
student *creatstudent(){
	student *p1, *p2, *head;
	int num = 0, score = 0, n = 0;
	head = NULL;
	p1 = p2 = (student*)malloc(sizeof(student));
	cout << "Input num:" << endl;
	cin >> p1->num;
	cout << "Input score:" << endl;
	cin >> p1->score;
	while (p1->num != 0 && p1->score != 0){
		n++;
		p2 = p1;
		if (n == 1){
			head = p1;
		}
		else{
			p1 = (student*)malloc(sizeof(student));
			p2->next = p1;
			cout << "Input num:" << endl;
			cin >> p1->num;
			cout << "Input score:" << endl;
			cin >> p1->score;
		}
	}
	p2->next = NULL;
	return head;
	delete p1, p2;
}

// 打印单向链表
void print(student *head){
	student *p = head;
	while (p != NULL){
		cout << p->num << endl;
		cout << p->score << endl;
		p = p->next;
	}
}

//查找到某一个数并删除
student *deleteNodes(student *head, int n){

	student *p1, *p2;
	p1 = p2 = head;
	if (head == NULL){
		return head;
	}
	else{
		if (head->num == n){
			head = head->next;
			delete p1;
			return head;
		}
		else{
			p1 = p1->next;
			while (p1->num != n && p1->next != NULL){
				p2 = p1;
				p1 = p1->next;
			}
			if (p1->num == n){
				p2->next = p1->next;
				delete p1;
				return head;
			}
			else{
				cout << "Not found!" << endl;
				return head;
			}
		}

	}

}


//链表按学号从小到大排好，现在插入一个数据
student *insertNodes(student *head, int n, int score){
	student *p1, *p0, *p2;
	p1 = p2 = head;
	p0 = (student *)malloc(sizeof(student));
	p0->num = n;
	p0->score = score;
	if (head == NULL){
		head = p0;
		head->next = NULL;
		return head;
	}
	else{

		if (p1->num >= n){
			p0->next = head;
			head = p0;
			return head;
		}
		p1 = p1->next;
		while (p1 != NULL && p1->num < n){
			p2 = p1;
			p1 = p1->next;
		}

		if (p1->num >= n)
		{
			p0->next = p1;
			p2->next = p0;
			return head;
		}
		else
		{
			p2->next = p0;
			p0->next = NULL;
			return head;
		}
	}

}

//打印反转链表并不反转链表
void printInveserly(student *head){

	stack<student *> nodes;
	student *p = head;
	while ( p!=NULL)          
	{
		nodes.push(p);
		p = p->next;
	}
	while (!nodes.empty())
	{
		p = nodes.top();
		cout << p->num << endl;
		cout << p->score<<endl;
	
		nodes.pop();	
	}
}

//反转链表
student * Inveserly(student *head){
	stack<student *> nodes;
	student *p,*p1;
	p= head;
	while (p != NULL)
	{
		nodes.push(p);
		p = p->next;
	}
	if (!nodes.empty()){
		head=p= nodes.top();
		nodes.pop();
	}
	while (!nodes.empty())
	{	
		p1 = nodes.top();
		p->next = p1;
		p = p1;
		nodes.pop();
	}
	p->next = NULL;
	return head;
}

//对链表进行排序（归并算法,num升序）
student* middle(student* head){

	student *p,*mid,*midl;
	p =mid= head;
	midl = NULL;
	while (p!=NULL&&p->next!=NULL)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             while (p != NULL&& p->next != NULL)
	{
		p = p->next->next;
		midl = mid;
		mid = mid->next;
	}
	
	midl->next = NULL;
	return mid;
}

student* merge(student *a, student *b){

	student *head, *p,*p1, *p2;
	p1 = a;
	p2 = b;
	if (a == NULL && b == NULL){
		return NULL;
	}
	else if (a == NULL&&b!=NULL){
		return b;
	}
	else if (a != NULL && b == NULL){
		return a;
	}
	else{

		if (p1->num <= p2->num){
			head=p = p1;
			p1 = p1->next;
		}
		else{
			head =p= p2;
			p2 = p2->next;
		}
		while (p1 != NULL&&p2 != NULL){
          
			if (p1->num <= p2->num){
				 p->next = p1;
				 p = p1;
				 p1 = p1->next;
			}
			else{
				p->next = p2;
				p = p2;
				p2 = p2->next;
			}

		}
		if (p2!= NULL){
			p->next = p2;
			p = p2;
			
		}
		else if(p1!=NULL){
			p->next = p1;
			p = p1;	
		}
	}
	
	return head;

}

student* mergeSort(student * head){
	student *a,*b;
	if (head == NULL || head->next == NULL){
		return head;
	}
	else {
		a = head;
		b = middle(head);
		a=mergeSort(a);
		b=mergeSort(b);

		return merge(a, b);
		
	}
	
}


void main(){
	student *list = creatstudent();
	cout << "链表：" << endl;
	print(list);
	list = deleteNodes(list, 5);
	cout << "删除后的链表：" << endl;
	print(list);
	list = insertNodes(list, 2, 20);

	cout << "插入后的链表：" << endl;
	print(list);
	cout << "反转打印链表：" << endl;
	printInveserly(list);
	cout << "反转链表：" << endl;
	Inveserly(list);
	print(list);
	system("pause");

	print(mergeSort(list));

	system("pause");
}