链表总结，链表的建立，输出，删除，插入

1.总的代码

#include
using namespace std;
using ll = long long;

struct stu{
	int id;
	int score;
	struct stu *next;
};

//链表的建立
struct stu *create(){
	struct stu *p1,*p2,*head;
	head = NULL;
	p1 = (struct stu*)malloc(sizeof(struct stu));
	p2 = p1;
	scanf("%d%d",&p1->id,&p1->score);
	while(p1 -> id != 0){
		if(head == NULL){
			head = p1;
		}
		else{
			p2 -> next = p1;
		}
		p2 = p1;
		p1 = (struct stu*)malloc(sizeof(struct stu));
		scanf("%d%d",&p1->id,&p1->score);
		//想象成4步p2追p1，p2先让它的next指向p1，然后自己飞到p1的位置上
		//p1又跑到下一个结点，读入那里的数据，这样循环
	}
	p2 -> next = NULL;
	return head;
}

//链表的输出
void print(struct stu *head){
	struct stu *p;
	p = head;
	do{
		printf("%d %d\n",p->id,p->score);
		p = p->next;
	}while(p != NULL);
}

//链表的删除
struct stu *del(struct stu *head,int num){
	struct stu *p1,*p2;
	p1 = head;
	if(head == NULL) {cout << "空链表";return head;}
	while(p1 -> id != num && p1->next != NULL){
		//未找到并且没到最后一个
		p2 = p1;//p2要跟着p1，后面有用
		p1 = p1 -> next;
	}
	if(p1 -> id == num){
		if(p1 == head) head = p1 -> next;//头节点特殊考虑
		else
		p2 -> next = p1 -> next;
	}
	else printf("没有");
	return head;
}

struct stu*insert(struct stu *head,struct stu *stu4){
	struct stu *p0,*p1,*p2;
	p0 = stu4;
	p1 = head;
	if(head == NULL){
		head = p0;
		p0 -> next = NULL;
	}
	else{
		while((p0 -> id > p1 -> id) && (p1 -> next != NULL)){
			p2 = p1;
			p1 = p1 -> next;
		}
	}
	if(p0 -> id <= p1 -> id){
		if(head == p1) head = p0;
		else p2 -> next = p0;
		p0 -> next = p1;//插入
	}
	else{
		p1 -> next = p0;
		p0 -> next = NULL;
	}
	return head;
}

int main(){
	struct stu *head;
	head = create();
	ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
	print(head);
	printf("\n");
	//删除4号
	head = del(head,4);
	print(head);
	printf("\n");
	//插入4号，分数改为80
	struct stu stu4;
	stu4.id = 4,stu4.score = 80;
	head = insert(head,&stu4);
	print(head);
	return 0;
}

2.链表的建立 

有注释的地方是我自己的碎碎念，就是我写链表的时候容易忘记写的地方

struct stu /*这里有个空格*/*create(){
	struct stu *p1,*p2,*head;
	head = NULL;
	p1 = (struct stu*)malloc(sizeof(struct stu));
	p2 = p1;//这句话是让p2先跟上p1
	scanf("%d%d",&p1 -> id,&p1 -> score);
	while(p1 -> id != 0){
		if(head == NULL) head = p1;
		else p2 -> next = p1;
		p2 = p1;
		p1 = (struct stu*)malloc(sizeof(struct stu));
		scanf("%d%d",&p1 -> id,&p1 -> score);
	}
	p2 -> next = NULL;//这里是让p2指向的那个node的指针指向空，因为此时
	//p2在表尾
	return head;
}

3.链表的输出

void print(struct stu *head){
	struct stu *p;
	p = head;
	do{
		printf("%d %d\n",p -> id,p -> score);
		p = p -> next;
	}while(p != NULL);//这里是p不为空，而不是p -> next不为空
}

4.链表的删除

struct stu *del(struct stu *head,int num){
	struct stu *p1,*p2;//只用p1和p2，插入时要用p0，p1，p
	p1 = head;
	if(head == NULL){printf("空链表");/*必须用分号隔开*/return head;}
	//先判断链表是不是空，然后就开始找，p2紧跟着p1
	while(p1 -> id != num && p1 -> next != NULL){
		p2 = p1;
		p1 = p1 -> next;
	}
	//找完后就只有两种情况，找到了或者没找到
	//找到了
	if(p1 -> id == num){
		//找到了也分三种，要删的数在表头，在表中间，在表尾
		if(p1 == head) head = p1 -> next;
		//在表中间和表尾的操作是一样的
		else{
			p2 -> next = p1 -> next;
		}
	}
	else printf("找不到");
	return head;
}
//总结一下，找的过程就是先设置一个p1，和一个p2，p1指向表头，判断表是否为空，然后开始找
//找完后再判断是否找到，找到又分为表头和其它这两种情况

5.链表的插入

struct stu *insert(struct stu *head,struct stu *stu4){
	//传入一个结构体指针用struct stu *stu4这样的格式
	struct stu *p0,*p1,*p2;
	p0 = stu4;//p0是用来存要插入的那个结构体的
	p1 = head;
	//第一种，没有节点,把插入的那个点作为第一个节点
	if(head == NULL) head = p0,p0 -> next = NULL;
	//第二种，存在节点
	else
	//开始找
	//要插入的那个结构体的id大于当前的id就不断往后找
		while(p0 -> id > p1 -> id && p1 -> next != NULL){
			p2 = p1;
			p1 = p1 -> next;
		}
	//又分三种，插入的在表头，在表中，在表尾
	//其中在表头和表中操作相同
	if(p0 -> id <= p1 -> id){
		if(p1 == head) head = p0;
		else p2 -> next = p0;
		p0 -> next = p1;
	}
	else {p1 -> next = p0;p0 -> next = NULL;}
	return head;
}