在單鏈表當中，從已知節點出發，只能訪問該節點的後繼節點，卻無法訪問

該節點之前的節點，在單循環鏈表當中，雖然可以通過一個節點訪問表中所

有節點，但是要找到直接前驅卻要遍歷整個表，因此為了加快尋找某個節點

的前驅，可以在每個節點的結構體上添加一個直接訪問前驅的指針域來快速

定位前驅節點。下面是簡單的雙鏈表代碼，當然優勢還沒有體現出來，後面

在慢慢補充

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

#define OK 1
#define ERROR 0
#define OVERFLOW -1

typedef 
 
struct Dbnode{
  int data;
  struct Dbnode * next;
  struct Dbnode * prior;
} Dbnode, *Dblink;

typedef int ElemType;
typedef int Status;

Status initLink(Dblink * link,int num){
  srand(time(0));

  Dblink L = *link;
  Dblink tmp,new;
  L->data = 0;
  L->prior = NULL;
  L->next = NULL;
  tmp 
 
= L;

  int i;
  for(i=0;i<num;i++){
    new = (Dblink)malloc(sizeof(Dbnode));
    new->data = rand()%100 +1;
    new->next = tmp->next;
    new->prior = tmp;
    tmp->next = new;
    tmp = tmp->next;
  }

  return OK;
}

Status insertLink(Dblink *link,int index,ElemType e){

  Dblink tmp 
 
= (*link)->next;  //ignore head node
  Dblink new,pre;
 
  int i=1;
 
  while( tmp && i<index ){
     tmp = tmp->next;
     i++;
  }

  if( !tmp || i>index){
     printf("overflow\n");
     return OVERFLOW;
  }

  new = (Dblink)malloc(sizeof(Dbnode));
  pre = tmp->prior;

  new->data = e;
  new->prior=pre;
  new->next =tmp;
  pre->next = new;
  tmp->prior= new;
 
  return OK;
}

Status deleteLink(Dblink *link,int index){
 
  Dblink tmp = (*link)->next;  //ignore head node

  int i=1;
  while( tmp && i<index ){
    tmp=tmp->next;
    i++;
  }
 
  if( !tmp || i>index ){
     printf("overflow\n");
     return OVERFLOW;
  }

  Dblink pre = tmp->prior;
  Dblink net = tmp->next;
  pre->next = tmp->next;
  net->prior = tmp->prior;

  free(tmp);

  return OK;
}

Status printLink(Dblink link){
   Dblink p = link;
   while(p->next){
     p = p->next;        //ignore head node
     printf("[%d] ",p->data);
   }

   printf("\n");
   return OK;
}

int main(){
  int num,index,value;
  Dblink link = (Dblink)malloc(sizeof(Dbnode));

  //initation
  printf("[create]enter the num:");
  scanf("%d",&num);
  initLink(&link,num);
  printLink(link);

  //insert
  printf("[insert]enter the index:");
  scanf("%d",&index);
  printf("[insert]enter the value:");
  scanf("%d",&value);
  insertLink(&link,index,value);
  printLink(link);

  //delete
  printf("[delete]enter the index:");
  scanf("%d",&index);
  deleteLink(&link,index);
  printLink(link);
  return OK;
}

雙向鏈表代碼