2019-03-02-数据结构-单链表

数据结构—单链表

什么是链表？

首先，链表是一种线性的链式存储的数据结构，“链” 说明其特征，由一环一环也就是“节点”组成。
链表分三种：单链表、双向链表和循环链表。

单链表：节点1（Begin）->节点2->节点3->节点4->END

节点1为头，END为结束，也就说节点4为链表的尾 “->” 为链接的方式。
接下来我们来看代码的简单实现（进行了简单调试）。单链表为最简单的链表，我觉得重点在于"->"链接方式，掌握其链接方式可以用更加形象的图像形式理解。

链表与数组之间的差别在于，首先最明显的差别，数组在堆栈中的存储空间是连续的，链表是不连续的，这个节点在地址0x100，下一个节点可能跑到0x200去了。
因为链表的结构特性，其明显的优势在于插入，删除操作极其方便，而且快。同样的操作，用数组去实现就会显得复杂多。
但个人觉得，也有不够方便的地方，比如数组，我想用哪个就直接利用下标去取值即可，但是链表，你做不到，你必须遍历得去寻找他。
所以链表，数组，有利有弊，各自都有长处和短处，具体应用得看场合。毕竟大家都是一种数据的结构。

2019-03-02-single_link.jpg

/*************************************************************************
    > File Name: list.c
    > Author: westzhao 
    > Created Time: 2017/08/30 Wed 22:36:36
 ************************************************************************/

#include
#include
#include

typedef struct NODE
{
    int value;
    struct NODE *next;
}list;


int initList(list **head, int value);
int insertTail(list **node, int value);
int insertNode(list **node, int value, int position);
int deleteNode(list **node, int position);
int deleteList(list **head);
int getListLen(list **node);
int printList(list **head);


/*
 * Function: initList
 * Author: westzhao
 */
int initList(list **head, int value)
{
    *head = (list *)malloc(sizeof(list));
    if(*head == NULL)
    {
        printf("head node alloc failed!\r\n");
        return -1;
    }
    
    (*head)->value = value;
    (*head)->next = NULL;

    return 1;
}


/*
 * Function: insertTail
 *           insert new node at the tail of list
 * Author: westzhao
 */
int insertTail(list **node, int value)
{
    list *current;
    list *new;
    
    current = *node;
    
    /* find the last node */
    while(current->next != NULL && current != NULL)
    {
        current = current->next;
    }
    
    new = (list *)malloc(sizeof(list));
    if(new == NULL)
    {
        printf("new node alloc mem failed!\r\n");
        return -1;
    }
    
    new->value = value;
    new->next = NULL;

    if(current == NULL)
    {
        /* the list is empty add the head of the list */
        current = new;
    }
    else
    {
        current->next = new;
    }

    return 1;
}


/*
 * Function: insertNode
 *           insert new node by the position
 * Author: westzhao
 */
int insertNode(list **node, int value, int position)
{
    int current_pos;
    list *new;
    list *before;
    list *current;
    
    if(position <= 0)
    {
        printf("position:%d error\r\n", position);
        return -1;
    }
    
    current = *node;
    if(current == NULL)
    {
        printf("head node empty\r\n");
        return -1;
    }
    
    new = (list *)malloc(sizeof(list));
    if(new == NULL)
    {
        printf("new node alloc mem failed!\r\n");
        return -1;
    }

    for(current_pos = position; current_pos>0; current_pos--)
    {
        if(current != NULL)
        {
            before = current;
            current = current->next;
        }
    }

    new->value = value;
    
    before->next = new;
    new->next = current;

    return 1;
}


/*
 * Function: deleteNode
 *           delete the Node by position
 * Author: westzhao
 */
int deleteNode(list **node, int position)
{
    int current_pos;
    list *before;
    list *current;

    if(position == 0)
    {
        printf("position:%d error\r\n", position);
        return -1;
    }
    
    current = *node;
    if(current == NULL)
    {
        printf("head node empty\r\n");
        return -1;
    }
    
    for(current_pos = position; current_pos>0; current_pos--)
    {
        if(current != NULL)
        {
            before = current;
            current = current->next;
        }
        else
        {
            printf("pos:%d out of range\r\n", position);
            return -1;
        }
    }
    
    before->next = current->next;
    free(current);
    
    return 1;
}


/*
 * Function: deleteList
 *           delete all of the list
 * Author: westzhao
 */
int deleteList(list **head)
{
    int pos;
    list *current;
    
    if(*head == NULL)
    {
        printf("list head NULL\r\n");
        return -1;
    }
    
    pos = getListLen(head);
    current = *head;
    
    while(pos > 1)
    {
        deleteNode(¤t, pos-1);
        pos--;
    }
    
    free(current);
    *head = NULL;

    return 1;
}


/*
 * Function: getListLen
 *           get length of the list
 * Author: westzhao
 */
int getListLen(list **node)
{
    int length = 0;
    list *current;
    
    if(*node == NULL)
    {
        printf("list empty");
        return -1;
    }

    current = *node;
    while(current != NULL)
    {
        current = current->next;
        length ++;
    }

    return length;
}


/*
 * Function: printList
 *           print all of the list
 * Author: westzhao
 */
int printList(list **head)
{
    if(*head == NULL)
    {
        printf("list empty\r\n");
        return -1;
    }
    
    list *temp = *head;
    
    do
    {
        printf("%d\t", temp->value);
        temp = temp->next;
    }while(temp != NULL);

    printf("\r\n");

    return 1;
}


int main()
{
    list *head;
    
    initList(&head, 1);
    insertTail(&head, 12);
    insertTail(&head, 23);
    insertTail(&head, 100);
    insertNode(&head, 2, 1);
//  insertNode(&head, 2, 1);
//  insertNode(&head, 42, 2);
    //insertNode(&head, 12312, 7);
    printf("list len:%d \r\n", getListLen(&head));
    printList(&head);
    deleteNode(&head, 1);
    printf("list len:%d \r\n", getListLen(&head));
    printList(&head);
    deleteList(&head);
    printList(&head);

    return 0;
}