动态创建链表 与头插法 和头插法的优化

1.代码一

思想：在main函数中实行三次头插法，在insertFromHead（）函数中，主要创建新的节点new，开辟空间，输入想要增加的data；根据头节点的情况来判断插入，

如果head == NULL；head = new; 返回头节点 ;

如果不为空，新节点 new -> next = head; head = new ;返回头节点

#include<stdio.h>
#include<stdlib.h>
struct Test
{
        int data;
        struct Test *next;
};

void printLink(struct Test *head)
{
        struct Test *point;
        point = head;
        printf("output the new insert data:\n");
        while(point !=NULL){
                printf("%d ",point->data);
                point = point->next;
        }
        putchar('\n');
}

struct Test* insertFromHead(struct Test *head)
{
        struct Test *new;
new = (struct Test*)malloc(sizeof(struct Test));
        printf("Please input your new node data:\n");
        scanf("%d",&(new->data));
        if(head ==NULL)
        {
                head = new;
                return head;
        }else
        {
                new ->next = head;
                head = new;
        }
        return head;
}

int main()
{
        int i = 3;
        struct Test *head = NULL;
        while(i--){
                head = insertFromHead(head);
        }
  printLink(head);
        return 0;
}

2.代码二

优化思想：

        在insertFromHead()函数，用while（1）无限循环 输入， 当输入的data =0 时；终止输入，返回 head ，打印函数。

#include<stdio.h>
#include<stdlib.h>
struct Test
{
        int data;
        struct Test *next;
};

void printLink(struct Test *head)
{
        struct Test *point;
        point = head;
        printf("output the new insert data:\n");
        while(point !=NULL){
                printf("%d ",point->data);
                point = point->next;
        }
        putchar('\n');
}

struct Test* insertFromHead(struct Test *head)
{
        struct Test *new;
        while(1){
        new = (struct Test*)malloc(sizeof(struct Test));
        printf("Please input your new node data:\n");
        scanf("%d",&(new->data));
        if(new->data ==0){
                printf("0 quit\n");
                return head;
        }
        if(head ==NULL)
        {
                head = new;
        }else
        {
                new ->next = head;
                head = new;
        }
    }
        return head;
}

int main()
{
    
        struct Test *head = NULL;
  
        head = insertFromHead(head);

        printLink(head);
        return 0;
}

3.代码三

优化思想：创建链表和插入节点的两个功能用函数封装的方式分开，目的是有利于调用插入函数；

insertFromHead()  函数中，判断head是否为空，否则插入

creatLinkHead()  函数中，开辟new 节点的空间，在while(1)循环中，无限输入data,若data为0则跳出循环，不为0则调用插入函数insertFromHead（）

        另外，在动态创建链表的同时，''new''  ,可以用free()函数释放内存。

#include<stdio.h>
#include<stdlib.h>
struct Test
{
        int data;
        struct Test *next;
};

void printLink(struct Test *head)
{
        struct Test *point;
        point = head;
        printf("output the new insert data:\n");
        while(point !=NULL){
                printf("%d ",point->data);
                point = point->next;
        }
        putchar('\n');
}

struct Test* insertFromHead(struct Test *head,struct Test *new)
{
        if(head ==NULL)
        {
                head = new;
        }else
        {
                new ->next = head;
                head = new;
        }
        return head;
}

struct Test *creatLink(struct Test *head)
{
        struct Test *new;
        while(1){
                 new = (struct Test*)malloc(sizeof(struct Test));
                 printf("Please input your new node data:\n");
                 scanf("%d",&(new->data));
                 if(new->data ==0){
                         printf("0 quit\n");
                         free(new);
                         return head;
                 }
                head = insertFromHead(head,new);
        }
}

int main()
{
        struct Test *head = NULL;
        struct Test t1 = {1000,NULL};
        head = creatLink(head);
        printLink(head);
        head = insertFromHead(head,&t1);
        printLink(head);
        return 0;
}