链表（裸题）

Doubly Linked List  Aizu - ALDS1_3_C

Your task is to implement a double linked list.

Write a program which performs the following operations:

• insert x: insert an element with key x into the front of the list
• delete x: delete the first element which has the key of x from the list
• deleteFirst: delete the first element from the list
• deleteLast: delete the last element from the list

Input

The input is given in the following format:

n

command₁

command₂

...

command_n

In the first line, the number of operations n is given. In the following
n lines, the above mentioned operations are given in the following format:

• insert x
• delete x
• deleteFirst
• deleteLast

Output

Print all the element (key) in the list after the given operations. Two consequtive keys should be separated by a single space.

Constraints

• The number of operations ≤ 2,000,000
• The number of delete operations ≤ 20
• 0 ≤ value of a key ≤ 10⁹
• the number of elements in the list does not exceed 10⁶

Sample Input 1

7
insert 5
insert 2
insert 3
insert 1
delete 3
insert 6
delete 5

Sample Output 1

6 1 2

Sample Input 2

9
insert 5
insert 2
insert 3
insert 1
delete 3
insert 6
delete 5
deleteFirst
deleteLast

Sample Output 2

1

题目意思是指写一个支持插入元素，删除特定元素，删除头元素，删除尾元素，打印整条链表操作的链表。

下面是初始化操作:

然后是各种普通操作顺序：

在理解后就可以看代码了，本题为了快速的删除尾，所使用的是环型链表，上代码：

 1     #include <iostream>
 2     #include <cstdio>
 3     #include <cstring>
 4     #include <cstdlib>
 5     using namespace std;
 6
 7     struct Node{
 8       int key;
 9       Node *prev;
10       Node *next;
11     };
12
13     Node *head;
14
15     Node *listSearch(int key){
16       Node *cur = head->next;
17       while(cur != head && cur->key != key){
18         cur = cur->next;
19       }
20       return cur;
21     }
22
23     void init(){
24       head = new Node;
25       head->prev = head;
26       head->next = head;
27     }
28
29     void printlist(){
30       Node *cur = head->next;
31       int isf = 0;
32       while(1){
33         if(cur == head)break;
34         if(isf++ > 0)printf(" ");
35         printf("%d",cur->key);
36         cur = cur->next;
37       }
38       printf("\n");
39     }
40
41     void insert(int key){
42       Node *x = new Node;
43       x->key = key;
44       x->next = head->next;
45       head->next->prev = x;
46       head->next = x;
47       x->prev = head;
48     }
49
50     void deleteNode(Node *t){
51       if(t == head)return;
52       t->prev->next = t->next;
53       t->next->prev = t->prev;
54       free(t);
55     }
56
57     void deleteFirst(){
58       deleteNode(head->next);
59     }
60
61     void deleteLast(){
62       deleteNode(head->prev);
63     }
64
65     void deletekey(int key){
66       deleteNode(listSearch(key));
67     }
68
69     int main(){
70       int key,n,i;
71       char com[20];
72       scanf("%d",&n);
73       init();
74       for(i = 0;i < n; i++){
75         scanf("%s%d",com,&key);
76         if(com[0] == ‘i‘){insert(key);}
77         else if(com[0] == ‘d‘){
78           if(strlen(com) > 6){
79             if(com[6] == ‘F‘)deleteFirst();
80             else if(com[6] == ‘L‘)deleteLast();
81           }
82           else{
83             deletekey(key);
84           }
85         }
86       }
87       printlist();
88       return 0;
89     }