双链表学习

有了单链表的理解，双链表就好些了。双链表的遍历，查找某个结点和单链表比较相似。只是在删除和插入的时候要指明前后的指针 

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

typedef struct node {
    int data;
    struct node *pre;
    struct node *next;
}Node;




Node *create(int n)
{
    Node *head;
    head = (Node*)malloc(sizeof(Node));
    if(head==NULL)
        return;
    head->pre = NULL;
    head->next = NULL;
    Node *p = head;
    int i;
    for(i=0;i<n;i++)
    {
        Node *cur;
        cur = (Node*)malloc(sizeof(Node));
        if(cur==NULL)
            return;
        cur->data = i+1;
        p->next = cur;
        cur->pre = p;
        p = cur;
    }
    p->next = NULL;
    return head;

}





void print(Node *L)
{
    Node *cur = L->next;
    while(cur!=NULL)
    {
        printf("%d,",cur->data);
        cur = cur->next;
    }
    printf("\n");
}



Node *insert(Node *L,int k,int data)
{
    int i=1;
    Node *cur = L->next;
    while(i<k&&!cur)
    {
        cur = cur->next;
        printf("%d\n",cur->data);
        ++i;
    }

    if(cur==NULL||i>k)
        return;
    Node *insert_node;
    insert_node = (Node*)malloc(sizeof(Node));
    if(insert_node==NULL)
        return;
    //必须指明前后的指针
    insert_node->data = data;
    insert_node->pre = cur;
    insert_node->next = cur->next;
    cur->next->pre = insert_node;
    cur->next = insert_node;

    return L; 
}

Node *delete(Node *L,int k)
{
    Node *cur = L->next;
    if(!cur)
        return;
    int i=1;
    while(i<k&&cur!=NULL)
    {
        cur = cur->next;
        ++i;
    }
    if(i>k||!cur)
        return;
    //其实删除比较好理解。    
    cur->pre->next = cur->next;
    cur->next->pre = cur->pre;
    free(cur);
    return L;
}



int main(void)
{
    int n = 10;
    Node *L = create(n);
    print(L);
    Node *iL = insert(L,2,100);
    print(iL);
    Node *dL = delete(L,14);
    print(dL);
    return 0;
}
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