关于单链表的思考

当我看了这个例子后http://learn.akae.cn/media/ch26s01.html

感觉很简单没什么特别的（这感觉往往遗漏很多细节）。

例子中用了static 定义了关键字 static link head = NULL;

看到后我就想用非static来重写单链表。

习惯了Erlang的函数编程，在定义C语言中的函数时刻意不用指针去实现，为了进一步理解代码还刻意不用typedef定义变量。可是奋斗了很久也没实现。

不得不用取地址方式，最后也没实现。不得不用指针了，这样就造成了传输指针又返回指针了，对于C 语言这可是多此一举。

创建链表时是从表头插入的

 75 struct node * insert(struct node *node, char ch)

 76 {             

 77     struct node *node1 = create_node(ch); 

 78     node1->next = node;                                                                                                                                                                                         

 79     return node1;

 80 }

 81 

 82 struct node * create_node(char ch)

 83 {

 84     struct node *node = malloc(sizeof *node);

 85     node->element = ch;

 86     node->next = NULL;

 87     return node; 

 88 }

 

 

写完创建，又写了个删除但是删除不掉

154 struct node * no_delete_node(struct node *head, char ch)

155 {

156 

157     printf("no_delete_node2 head->data=%c\n", ch);                                                                                      

158     struct node *ret = head;

159     struct node *pre = head;                                                                                                                      

160     for(;pre; pre = pre->next){

161         if(pre->element==ch){

162             pre = pre->next;

163             return ret;

164         }

165     }

166     return ret;

167 }   

 

后来改成 （这代码实在在冗余了）就可以删除了，

关键就是 142 行                head->next = pre ->next->next;     这句代码实现了删除

125 struct node * delete_node(struct node *head, char ch)

126 {

127     printf("delete_node head->element=%c\n", head->element);

128     struct node *ret = head;

129     struct node *pre = head;

130     if(head == NULL){

131         return head; 

132     }else{

133         if(head->element == ch){

134             head = head ->next;

135             //ret = head->next;

136             return ret;

137         }

138         while(head->next != 0){

139             if(pre->next-> element == ch){

140                 struct node *node = pre->next;

141                 free_node(node);

142                head->next = pre ->next->next;    

143                 printf("found del %c\n", head ->element);

144             }else{

145                 printf("notfound del%c\n", head ->element);

146             }

147             pre = head->next;

148         }

149     }

150     return ret;

151 } 

152 

就可以删除了，

 

最后改成这样实现

171 struct node * delete_node2(struct node *head, char ch)

172 {   

173     

174     printf("delete_node2 head->data=%c\n", ch);                                                                                      

175     struct node **pre = &head;                                                                                                                      

176     for(;*pre; pre = &(*pre)->next){

177         if((*pre)->element==ch){

178             *pre = (*pre)->next;

179             return head;

180         }

181     }

182     return head;

183 }   

相比较delete_node2 代码简洁多了，乍看上跟no_delete_node方法差不多，本质上却不同。

no_delete_node2并没有删除节点。delete_node2则利用取地址的方式实现，这正是C语言地址指针的妙处。

刚开始想到在node再加一个属性前驱节点，但这已经不是原先数据结构了。

 

delete_node2

 

 no_delete_node

 

 

 

link3.c
#include <stdio.h>
struct  node{
    char  element;
    struct  node *next;
};

struct  node * create_node( char  ch);
void    free_node( struct  node *node);
struct  node * search_node( struct  node *node,  char  ch);
struct  node * insert ( struct  node *node,  char  ch);
struct  node * delete_node( struct  node *node,  char  ch);
struct  node * delete_node2( struct  node *node,  char  ch);
struct  node * delete_node4( struct  node *node,  char  ch);
struct  node * no_delete_node( struct  node *head,  char  ch);
void    destroy( struct  node *node);
void  traverse( void  (*visit)( struct  node *),  struct  node *head);
void  print_item( struct  node *p);
struct  node * push( struct  node *node,  char  ch);
struct  node * pop( struct  node *node);

void  list_link( struct  node  *node);
void  list_link2( struct  node  *node);

void  main( void )
{
    struct  node *node = create_node( 'a' );
    struct  node *found_node =  malloc ( sizeof (*found_node));
    struct  node *c_node =  malloc ( sizeof (*c_node));
    printf ( "node->element=%c\n" , node->element);
    node = insert(node,  'b' );
    printf ( "node->element=%c\n" , node->element);
    node = insert(node,  'c' );
    printf ( "node->element=%c\n" , node->element);
    node = insert(node,  'd' );
    printf ( "node->element=%c\n" , node->element);
    node = insert(node,  'e' );
    printf ( "node->element=%c\n" , node->element);


    found_node = search_node(node,  'c' );
    //free_node(found_node);
    printf ( "found_node->element=%c\n" , found_node->element);
    puts ( "before\n" );
    list_link2(node);
    puts ( "del\n" );
    c_node = delete_node2(node,  'b' );
    //c_node = no_delete_node(node, 'b');
    puts ( "after ret c_node \n" );
    list_link(c_node);
    puts ( "after node \n" );
    list_link(node);
    //puts("destroy node \n");
    //destroy(node);
    //list_link(node);
    traverse(print_item, node);
}


void  list_link2( struct  node  *head)
{
    while (head){
        printf ( "%c\n" , head ->element);
        head = head ->next;
    }
}


void  list_link( struct  node  *node)
{
    printf ( "%c\n" , node->element);
    struct  node *head = node;
    while (head->next){
        head = head ->next;
        printf ( "%c\n" , head ->element);
    }
}

struct  node * insert( struct  node *node,  char  ch)
{
    struct  node *node1 = create_node(ch);
    node1->next = node;
    return  node1;
}

struct  node * create_node( char  ch)
{
    struct  node *node =  malloc ( sizeof  *node);
    node->element = ch;
    node->next = NULL;
    return  node;
}

struct  node * search_node( struct  node *head,  char  ch)
{
    struct  node *pre = head;
    if (pre == NULL){
        return  NULL;
    } else {
        while (pre != NULL){
            if (pre -> element == ch){
                printf ( "found pre->element=%c\n" , pre ->element);
                return  pre;
            }
            pre = pre->next;
        }
        return  NULL;
    }
}


struct  node * delete_node( struct  node *head,  char  ch)
{
    printf ( "delete_node head->element=%c\n" , head->element);
    struct  node *ret = head;
    struct  node *pre = head;
    if (head == NULL){
        return  head;
    } else {
        if (head->element == ch){
            head = head ->next;
            return  ret;
        }
        while (head->next != 0){
            if (pre->next-> element == ch){
                struct  node *node = pre->next;
                free_node(node);
                head->next = pre ->next->next;
                printf ( "found del %c\n" , head ->element);
            } else {
                printf ( "notfound del%c\n" , head ->element);
            }
            pre = head->next;
        }
    }
    return  ret;
}


struct  node * no_delete_node( struct  node *head,  char  ch)
{

    printf ( "no_delete_node2 head->data=%c\n" , ch);
    struct  node *ret = head;
    struct  node *pre = head;
    for (;pre; pre = pre->next){
        if (pre->element==ch){
            pre = pre->next;
            return  ret;
        }
    }
    return  ret;
}



struct  node * delete_node2( struct  node *head,  char  ch)
{

    printf ( "delete_node2 head->data=%c\n" , ch);
    struct  node **pre = &head;
    for (;*pre; pre = &(*pre)->next){
        if ((*pre)->element==ch){
            *pre = (*pre)->next;
            return  head;
        }
    }
    return  head;
}

struct  node * delete_node4( struct  node *head,  char  ch)
{
    printf ( "delete_node4 head->data=%c\n" , ch);
    struct  node *ret = head;
    struct  node *pre = head;

    while (NULL != pre->next)
    {
        if (pre->next->element == ch)
        {
            printf ( "found del %c\n" , pre->next->element);
            pre->next = pre ->next->next;

        } else  pre = pre->next;
    }
    return  ret;
}


void  free_node( struct  node *node)
{

    free (node);
}

void    destroy( struct  node *head)
{
    struct  node *del = head;
    while (head){
        del = head;
        head = head-> next;
        free_node(del);
    }
}

void  traverse( void  (*visit)( struct  node *),  struct  node *head)
{
    puts ( "traverse  \n" );
    while (head){
        printf ( "traverse %c\n" , head->element);
        head = head->next;
    }

}

void  print_item( struct  node *p)
{
    printf ( "%c\n" , p->element);
}

struct  node * push( struct  node *node,  char  ch)
{
    return  insert(node, ch);
}

struct  node * pop( struct  node *head)
{

}

link2.c

#include <stdio.h>

struct  node{
    char  element;
    struct  node *next;
};

struct  node * create_node( char  ch);
struct  node * delete_node( struct  node *node,  char  ch);
struct  node * delete_node4( struct  node *node,  char  ch);
struct  node * search_node( struct  node *node,  char  ch);
struct  node * insert ( struct  node *node,  char  ch);

void  list_link( struct  node  *node);

void  main( void )
{
    struct  node *c_node =  malloc ( sizeof (*c_node));

    struct  node *node = create_node( 'a' );
    struct  node *node2 = node;
    printf ( "node->element=%c\n" , node->element);
    node = insert(node,  'b' );
    printf ( "node->element=%c\n" , node->element);
    node = insert(node,  'c' );
    printf ( "node->element=%c\n" , node->element);
    node = insert(node,  'd' );
    printf ( "node->element=%c\n" , node->element);
    node = insert(node,  'e' );

    //found_node = search_node(node, 'b');
    //printf("found_node->element=%c\n", found_node->element);
    puts ( "before\n" );
    list_link(node);
    puts ( "del\n" );
    c_node = delete_node4(node,  'b' );
    puts ( "after c_node\n" );
    list_link(c_node);
    puts ( "after list node\n" );
    list_link(node);
    puts ( "after list node2\n" );
    list_link(node2);
    //printf("%d\n", node.next);
}

void  list_link( struct  node  *node)
{
    printf ( "%c\n" , node->element);
    struct  node *head = node;
    while (head->next != 0){
        head = head ->next;
        printf ( "%c\n" , head ->element);
    }
}

struct  node * insert( struct  node *head,  char  ch)
{
    struct  node *node1 = create_node(ch);
    node1->next = head;
    return  node1;
}

struct  node * create_node( char  ch)
{
    struct  node *head = ( struct  node *) malloc ( sizeof ( struct  node));
    head->element = ch;
    head->next = NULL;
    return  head;
}

struct  node * search_node( struct  node *head,  char  ch)
{
    struct  node *pre = head;
    if (pre == NULL){
        return  NULL;
    } else {
        while (pre != NULL){
            if (pre -> element == ch){
                printf ( "found pre->element=%c\n" , pre ->element);
                return  pre;
            }
            pre = pre->next;
        }
        return  NULL;
    }
}


struct  node * delete_node( struct  node *head,  char  ch)
{
    printf ( "delete_node head->element=%c\n" , head->element);
    struct  node *ret = head;
    struct  node *pre = head;
    if (pre == NULL){
        return  ret;
    } else {
        if (pre->element == ch){
            pre = pre ->next;
            return  ret;
        }
        while (pre->next != NULL){
            printf ( "----- %c\n" , pre ->element);
            if (pre->next-> element == ch){
                printf ( "found del %c\n" , pre ->element);
                struct  node *del = pre->next;
                free (del);
                pre->next = pre ->next->next;
            } else {
                printf ( "notfound del%c\n" , pre ->element);
            }
            pre = pre->next;
        }
    }
    return  ret;
}



struct  node * delete_node4( struct  node *head,  char  ch)
{
  printf ( "delete_node4 head->data=%d\n" , ch);
  struct  node *ret = head;
  struct  node *pre = head;
  while (NULL != pre->next)
  {
      if (pre->next->element == ch)
      {
          printf ( "found del %d\n" , pre->next->element);
          pre->next = pre ->next->next;

      }
      else  pre = pre->next;
  }
  return  ret;
}