c语言之单链表的创建及排序

　今天对之前学习过的链表知识进行简单的总结顺便写点代码；创建一个链表有头插法跟尾插法两种，在下面代码中我们为结点分配的内存实在堆上分配的，因此需要我们手动释放，释放用free（）函数

　下面代码贴出具体代码：

　

 #include <stdio.h>
 #include <stdlib.h>

 struct person {
     int age;
     struct person *next;
 };

 struct person *insert_head(struct person *head, int age);
 struct person *insert_tail(struct person *head, int age);
 void destroy_list(struct person *head);
 void show(struct person *head);

 int main()
 {
     struct person *head = NULL;
     head = insert_tail(head, );
     head = insert_tail(head, );
     head = insert_tail(head, );
     head = insert_tail(head, );
     head = insert_tail(head, );
     show(head);

　　　return ；
 }

 /*头插法*/
 struct person *insert_head(struct person *head, int age)
 {
     struct person *tmp = NULL;

     tmp = (struct person *)malloc(sizeof(struct person));
     tmp->age = age;
     tmp->next = NULL;

     if(NULL == head) {
         return tmp;
     }
     tmp->next = head;
     head = tmp;

     return head;
 }

 /*尾插法*/
 struct person *insert_tail(struct person *head, int age)
 {
     struct person *tmp = NULL;
     struct person *find = NULL;

     tmp = (struct person *)malloc(sizeof(struct person));
     tmp->age = age;
     tmp->next = NULL;

     if(NULL == head) {
         return tmp;
     }
     find = head;
     while(find->next) {
         find = find->next;
     }
     find->next = tmp;

     return head;
 }

 /*销毁整个链表*/
 void destroy_list(struct person *head)
 {
     struct person *tmp = NULL;

     tmp = head->next;
     while(tmp) {
         head->next = tmp->next;
         free(tmp);
         tmp = head->next;
     }
 }

 /*遍历链表*/
 void show(struct person *head)
 {
     struct person *tmp = head;
     while(tmp) {
         printf("aeg is %d\n", tmp->age);
         tmp = tmp->next;
     }
 }

　　上面的是创建了一个简单的链表，下面我们对链表进行简单的排序：

　　对于下面的链表排序：我们可以分为三步：

　　（1）在原链表中找到最小的

　　（2）从原链表摘下最小的

　　（3）一次插入到新链表

　　循环直到原链表为空

 #include <stdio.h>
 #include <stdlib.h>

 struct person {
     int age;
     struct person *next;
 };

 struct person *insert_head(struct person *head, int age);
 struct person *insert_tail(struct person *head, int age);
 struct person *insert_sort(struct person *head);
 void destroy_list(struct person *head);
 void show(struct person *head);

 int main()
 {
     struct person *head = NULL;
     head = insert_tail(head, );
     head = insert_tail(head, );
     head = insert_tail(head, );
     head = insert_tail(head, );
     head = insert_tail(head, );
     show(head);
     printf("------------------------------\n");
     head = insert_sort(head);
     show(head);
 }

 /*头插法*/
 struct person *insert_head(struct person *head, int age)
 {
     struct person *tmp = NULL;

     tmp = (struct person *)malloc(sizeof(struct person));
     tmp->age = age;
     tmp->next = NULL;

     if(NULL == head) {
         return tmp;
     }
     tmp->next = head;
     head = tmp;

     return head;
 }

 /*尾插法*/
 struct person *insert_tail(struct person *head, int age)
 {
     struct person *tmp = NULL;
     struct person *find = NULL;

     tmp = (struct person *)malloc(sizeof(struct person));
     tmp->age = age;
     tmp->next = NULL;

     if(NULL == head) {
         return tmp;
     }
     find = head;
     while(find->next) {
         find = find->next;
     }
     find->next = tmp;

     return head;
 }

 /*销毁整个链表*/
 void destroy_list(struct person *head)
 {
     struct person *tmp = NULL;

     tmp = head->next;
     while(tmp) {
         head->next = tmp->next;
         free(tmp);
         tmp = head->next;
     }
 }

 #if 0
 /*从大到小*/
 struct person *insert_sort(struct person *head)
 {
     struct person *tmp = NULL;
     struct person *newhead = NULL;
     struct person *min = NULL;
     struct person *min_pre = NULL;

     if(NULL == head || NULL == head->next)
         return head;

     while(head) {
         tmp = head;
         min = head;
         min_pre = NULL;

         /*step 1:find min*/
         while(tmp->next) {
             if(min->age > tmp->next->age) {
                 min_pre = tmp;
                 min = tmp->next;
             }
             tmp = tmp->next;
         }

         /*step 2: cut min*/
         if(min == head) {
             head = head->next;
             min->next = NULL;
         }
         else {
             min_pre->next = min->next;
             min->next = NULL;
         }

         /*step 3: insert new list*/
         if(NULL == newhead) {
             newhead = min;
             continue;
         }
         min->next = newhead;
         newhead = min;
     }

     return newhead;
 }

 #else
 /*从小到大*/
 struct person *insert_sort(struct person *head)
 {
     struct person *tmp = NULL;
     struct person *newhead = NULL;
     struct person *newtail = NULL;
     struct person *min = NULL;
     struct person *min_pre = NULL;

     if(NULL == head || NULL == head->next)
         return head;

     while(head) {
         tmp = head;
         min = head;
         min_pre = NULL;

         /*step 1: find min*/
         while(tmp->next) {
             if(min->age > tmp->next->age) {
                 min_pre = tmp;
                 min = tmp->next;
             }
             tmp = tmp->next;
         }

         /*step 2: cut min*/
         if(min == head) {
             head = head->next;
             min->next = NULL;
         }
         else {
             min_pre->next = min->next;
             min->next = NULL;
         }

         /*step 3: insert new list*/
         if(NULL == newhead) {
             newhead = min;
             newtail = min;
             continue;
         }
         newtail->next = min;
         newtail = newtail->next;
     }

     return newhead;
 }
 #endif

 /*遍历链表*/
 void show(struct person *head)
 {
     struct person *tmp = head;
     while(tmp) {
         printf("aeg is %d\n", tmp->age);
         tmp = tmp->next;
     }
 }