linux c语言环境 非循环单链表实际应用示例

一、代码:

#include <stdio.h>
#include <stdlib.h>
#define _ULL unsigned long long

/*definition of single link:each node can only visit it's next node, and visit it's pre node,the last link point to NULL*/
/*use scene:sort number. get the minnest number from R[0]~R[n-1] and swap with R[0]; compare with other sort method*/

//Link is a struct which has a ull type and a Link * pointer type; mylink is a new name of struct Link by use of typedef
typedef struct Link
{
    _ULL value;
    struct Link *next;    
}mylink;

/*
quantity: init a mylink which has quantity number; add by tail;
https://blog.youkuaiyun.com/qq_52607834/article/details/115922172
*/
mylink* init_mylink(_ULL quantity)
{
    printf("begin to init...\n");
    _ULL i = 0;
    mylink* head_node = (mylink*)malloc(sizeof(mylink)); //init a head node
    head_node->value=0;
    printf("in init_mylink, i:%d\n", i);
    
    mylink* p_cursor_node = head_node; //a cursor pointer point to head_node
    for(i = 1; i < quantity; i ++)
    {
        /*
        create a new pointer and point it to an assigned value
        each tmp_mylink has two addresses: an address of itself + an address point to other link node
        */
        mylink* tmp_mylink = (mylink*)malloc(sizeof(mylink)); //malloc a new pointer
        tmp_mylink->value = i;     //value assignment
        tmp_mylink->next = NULL;   //pointer assignment
        printf("in init_mylink, i:%d\n", i);
        
        //point old pointer to new pointer, add by tail
        p_cursor_node->next = tmp_mylink; 
        p_cursor_node=tmp_mylink; //p_cursor_node point to new added node
        tmp_mylink->next = NULL;
    }
    return head_node;
}

void free_mylink(mylink* head_node)
{
    printf("begin to free...\n");
    int i = 0;
    mylink* p_cursor_node = head_node;
    //mylink* new_head_node = NULL;
    while(NULL != p_cursor_node)
    {
        head_node = head_node->next;
        free(p_cursor_node);
        printf("free %dth inode success!\n", i++);
        p_cursor_node = head_node;
    }
}
void print_mylink(mylink* head_node)
{
    int i = 0;
    mylink* p_cursor_node = head_node;
    while(NULL != p_cursor_node)
    {
        printf("the %dth inode's value:%llu\n", i++, p_cursor_node->value);
        p_cursor_node = p_cursor_node->next;
    }        
}

/*add a value,after add,all value are also sorted*/
void add_mylink_sort(mylink* head_node, _ULL value)
{
    int i = 0;
    _ULL pre_pos = 0, next_value = -1;
    mylink* p_cursor_node = head_node;
    while(NULL != p_cursor_node)
    {
        //printf("the %dth inode's value:%llu, pre node's value:%llu\n", i, p_cursor_node->value, next_value);       
        pre_pos = i;
        if(NULL != p_cursor_node->next)
            next_value = (p_cursor_node->next)->value;

        if(value >= p_cursor_node->value && value <= next_value)
        {
            mylink* add_node = (mylink*)malloc(sizeof(mylink)); //init a to-be-added node
            add_node->value = value;
            
            add_node->next = p_cursor_node->next;
            p_cursor_node->next = add_node; 
            return;
        }
        p_cursor_node = p_cursor_node->next;
    }        
}
void del_mylink_sort(mylink** head_node, _ULL value)
{
    int i = 0;
    mylink* p_cursor_node = *head_node;
    mylink* tmp_pre_node = NULL;
    while(NULL != p_cursor_node)
    {
        //printf("the %dth inode's value:%llu\n", i++, p_cursor_node->value);
        if(value == p_cursor_node->value)
        {
            if(NULL == tmp_pre_node)
            {
                printf("del %dth node in the head\n", i);
                *head_node = p_cursor_node->next;
                tmp_pre_node = *head_node;
                p_cursor_node->next = *head_node;
            }
            else
            {
                printf("del %dth node in the middle.\n", i);
                tmp_pre_node->next = p_cursor_node->next;
                p_cursor_node->next = tmp_pre_node->next;
            }
            
            //no need traverse to the last node in a sorted link
            if(value < (p_cursor_node->next)->value)
                return;
        }
        else
        {
            tmp_pre_node = p_cursor_node;
        }
        p_cursor_node = p_cursor_node->next;
        i ++;
    }    
}

void main(int argc, char *argv[])
{
    if(argc < 2)
    {
        printf("should follow by one para\n");
        exit(0);
    }
    mylink *mylink1 = NULL;      // compile passed
    /*Link *mylink2 = NULL;*/           // compile not passed, unknow type of 'Link', unless use struct Link
    
    //step 1: init a single node link
    mylink1 = init_mylink(atoi(argv[1]));
    if(NULL == mylink1)
    {
        printf("init_mylink failed\n");
        return;
    }
    
    //step 2:print all node link
    print_mylink(mylink1);
    
    //step 3:add a new node in middle of link, all value should Sort from small to large after insert
    printf("add 3...\n");
    add_mylink_sort(mylink1, 3);
    print_mylink(mylink1);
    
    //step 4:delete a node in middle of link,  all value should Sort from small to large after delete
    printf("del 3...\n");    
    del_mylink_sort(&mylink1, 3);
    print_mylink(mylink1);
    
    printf("del 0...\n");    
    del_mylink_sort(&mylink1, 0);
    print_mylink(mylink1);    
    
    //step 5:free node link
    free_mylink(mylink1);
}

二、运行环境:linux 64

三、编译方法:gcc single_link_list.c -g

四、运行及结果:

[root@localhost single_link_list]# ./a.out 5
begin to init...
in init_mylink, i:0
in init_mylink, i:1
in init_mylink, i:2
in init_mylink, i:3
in init_mylink, i:4
the 0th inode's value:0
the 1th inode's value:1
the 2th inode's value:2
the 3th inode's value:3
the 4th inode's value:4
add 3...
the 0th inode's value:0
the 1th inode's value:1
the 2th inode's value:2
the 3th inode's value:3
the 4th inode's value:3
the 5th inode's value:4
del 3...
del 3th node in the middle.
del 4th node in the middle.
the 0th inode's value:0
the 1th inode's value:1
the 2th inode's value:2
the 3th inode's value:4
del 0...
del 0th node in the head
the 0th inode's value:1
the 1th inode's value:2
the 2th inode's value:4
begin to free...
free 0th inode success!
free 1th inode success!
free 2th inode success!

五、对单向链表的理解：单向链表相比于双向链表能使用的场景很少。以上是一个用单向链表实现数字排序的算法。相比于数组，单向链表在插入和删除时只需要挪动1,2个指针的指向即可。

六、del_mylink_sort函数中传入了指向指针的指针，目的是为了能直接修改头结点的地址。

七、单向链表最难理解的是每个结点其实有两个地址：一个是自身的地址，一个是指向下一个结点的地址，理解了这个，才能根据画图写出自身指针和next指针之间的赋值。