国庆作业day2

#include 
typedef struct link
{
	union{
		char data;
		int len;
	};
	struct link *pre;
	struct link *next;
}link_list, *ptr;
 
//创建头节点
ptr create_head()
{
	ptr H = (ptr)malloc(sizeof(link_list));
	if(NULL == H){
		printf("地址申请失败\n");
		return NULL;
	}
	H->len = 0;
	H->pre = NULL;
	H->next = NULL;
	return H;
}
 
//创建节点
ptr create_node(char data)
{
	ptr L = (ptr)malloc(sizeof(link_list));
	if(NULL == L){
		printf("地址申请失败\n");
		return NULL;
	}
	L->data = data;
	L->pre = NULL;
	L->next = NULL;
	return L;
}
 
//头插
int insert_head(ptr H, char data)
{
	if(NULL == H){
		printf("入参为空\n");
		return -1;
	}
	ptr new = create_node(data);
	new->next = H->next;
	if(H->next != NULL){
		H->next->pre = new;
	}
	H->next = new;
	new->pre = H;
	H->len++;
	return 0;
}
 
//尾删
int delet_tail(ptr H)
{
	if(NULL == H){
		printf("入参为空\n");
		return -1;
	}
	if(H->next == NULL){
		printf("双向链表为空\n");
		return -2;
	}
	ptr del = H;
	while(del->next != NULL){
		del = del->next;
	}
	printf("%c->", del->data);
	del->pre->next = del->next;
	free(del);
	del = NULL;
	H->len--;
	return 0;
}
 
//输出
int output(ptr L)
{
	ptr p = L->next;
	while(p != NULL){
		printf("%c->",p->data);
		p = p->next;
	}
	return 0;
}
int main(int argc, const char *argv[])
{
	ptr L = create_head();
	char i = 0;
	for(i = 'a'; i <= 'z'; i++){
		insert_head(L, i);
	}
	for(i = 'a'; i <= 'z'; i++){
		delet_tail(L);
	}
	putchar(10);
	L = NULL;
	return 0;
}