c实现按访问频度非递增有序的带头节点的双向链表检索关键字

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

typedef struct doublenode
{
	char key;
	int freq;
	struct doublenode *pre,*next; 
} DoubleLinkNode,*DoubleLinkList;

DoubleLinkList loc(DoubleLinkList head, char x)
{
	DoubleLinkList p,q;
	p = head->next;
	head->key = x;
	while(p->key != head->key) p = p->next;
	if(p == head) //找不到关键字的节点 。新建个节点插在头结点前面 
	{
		q = (DoubleLinkList)malloc(sizeof(DoubleLinkNode));
		q->key = x;
		q->freq = 0;
		q->next = p;
		q->pre = p->pre ;
		p->pre->next = q;
		p->pre = q;
	}
	else 
	{
		q = p;
		q->freq++;
		head->freq = q->freq;// head指针的频度要修改，否则下面的while跳不出去 
		
		while(q->freq > p->pre->freq) p = p->pre;//找到当前q应该存放在的位置。p始终指向链表中比当前q频度小的最前面指针 
		if(p != q)
		{
			//先断开q 
			q->pre->next = q->next;
			q->next->pre = q->pre;
			//再把q挂到p前面 
			q->next = p;
			q->pre = p->pre;
			p->pre->next = q;
			p->pre = q;
		}		
	} 
		printf("\nfinally:");
		p = head->next;
	while(p != head)	
	{	
		printf("(%c,%d)",p->key,p->freq);
		p = p->next;
	}
	return head;
}

DoubleLinkList createdoublelinklist(char c[],int r[],int n)
{
	DoubleLinkList head,p,q;
	int i;
	head = (DoubleLinkList)malloc(sizeof(DoubleLinkNode));
	head->next = head;
	head->pre = head;
	p = head->next;
	if(n>0)
	{
		for(i = 0; i < n; i++)
		{
			while(p->next != head) p = p->next;
			q = (DoubleLinkList)malloc(sizeof(DoubleLinkNode));
			q->key = c[i];
			q->freq = r[i];
			
			q->pre = p;
			q->next = p->next;
			p->next->pre = q;
			p->next = q;			
		}
		
	}
		printf("original:");
		p = head->next;
	while(p != head)	
	{
	
		printf("(%c,%d)",p->key,p->freq);
			p = p->next;
	}
	return head;
}
int main()
{
	DoubleLinkList head;
	char x,c[5]={'a','b','c','d','e'};
	int r[5] = {5,3,3,2,1};
	head = createdoublelinklist(c,r,5);
	loc(head,'a');
	loc(head,'f');
	loc(head,'c');
	
	return 0;	
}