Doubly Linked List，（ Aizu

题目链接 ： https://vjudge.net/problem/Aizu-ALDS1_3_C

注 ：双向链表

#include<stdio.h>
#include<stdlib.h>
#include<string.h> 
struct Node{
    int key;
    struct Node *prior,*next;
};

Node *nil; //创建头节点 

Node* list_search(int key) {          //搜索链返回值为节点地址 
    Node *cur = nil -> next;
    while(cur -> key != key && cur != nil) {      //当key值与链中某节点key相同或到达nil停止 
        cur = cur -> next;
    } 
    return cur;    
}

void init() {                              //初始化头节点 
    nil = (Node *)malloc(sizeof(Node));    //定义一个指针不为其分配内存，需要动态分配内存 
    nil -> next = nil;
    nil -> prior = nil;
}

void print_list() {                        //打印链表 
    Node *cur = nil -> next;            //从首节点开始打印 
    int isf = 0;                        //判断空格输出 
    while(1) {
        if(cur == nil) break;
        if(isf++ > 0) printf(" ");
        printf("%d",cur ->key);
        cur = cur -> next; 
    }
    printf("
");
}
void delete_node(Node *t) {
    if (t == nil) return; //t为头节点不做处理
    t -> prior -> next = t -> next;
    t -> next -> prior = t -> prior; 
    free(t);                      //删除后释放空间 
}

void delete_frist() {
    delete_node(nil -> next);
}

void delete_last() {
    delete_node(nil -> prior);
}

void insert(int key) {                     //理解插入方式 
    Node *x = (Node*)malloc(sizeof(Node));
    x -> key = key;
    x -> next = nil -> next;
    nil -> next -> prior = x;
    nil -> next = x;
    x -> prior = nil;
}

void delete_key(int key) {
    delete_node(list_search(key));
}
int main()
{
    int key, n, i;
    int size = 0;
    char com[20];
    int np = 0,nd = 0;
    scanf("%d",&n);
    init();
    for (i = 0;i < n;i++ ) {
        scanf("%s%d",com,&key);
        if (com[0] == 'i') { insert(key);np++;size++; }
        else if(com[0] == 'd') {
            if (strlen(com) > 6){
                if( com[6] == 'F' ) delete_frist();
                else if( com[6] == 'L') delete_last(); 
                }
            else{
                delete_key(key); nd++;
            }
            size--;
            }
        }
    
    
    print_list() ;
    
    return 0;
 }