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：

    #include <iostream>  
    #include <cstdio>  
    #include <cstring>  
    #include <cstdlib>  
    using namespace std;  
      
    struct Node{  
      int key;  
      Node *prev;  
      Node *next;  
    };  
      
    Node *head;  
      
    Node *listSearch(int key){  
      Node *cur = head->next;  
      while(cur != head && cur->key != key){  
        cur = cur->next;  
      }  
      return cur;  
    }  
      
    void init(){  
      head = new Node;  
      head->prev = head;  
      head->next = head;  
    }  
      
    void printlist(){  
      Node *cur = head->next;  
      int isf = 0;  
      while(1){  
        if(cur == head)break;  
        if(isf++ > 0)printf(" ");  
        printf("%d",cur->key);  
        cur = cur->next;  
      }  
      printf("\n");  
    }  
      
    void insert(int key){  
      Node *x = new Node;  
      x->key = key;  
      x->next = head->next;  
      head->next->prev = x;  
      head->next = x;  
      x->prev = head;  
    }  
      
    void deleteNode(Node *t){  
      if(t == head)return;  
      t->prev->next = t->next;  
      t->next->prev = t->prev;  
      free(t);  
    }  
      
    void deleteFirst(){  
      deleteNode(head->next);  
    }  
      
    void deleteLast(){  
      deleteNode(head->prev);  
    }  
      
    void deletekey(int key){  
      deleteNode(listSearch(key));  
    }  
      
    int main(){  
      int key,n,i;  
      char com[20];  
      scanf("%d",&n);  
      init();  
      for(i = 0;i < n; i++){  
        scanf("%s%d",com,&key);  
        if(com[0] == 'i'){insert(key);}  
        else if(com[0] == 'd'){  
          if(strlen(com) > 6){  
            if(com[6] == 'F')deleteFirst();  
            else if(com[6] == 'L')deleteLast();  
          }  
          else{  
            deletekey(key);  
          }        
        }  
      }  
      printlist();  
      return 0;  
    }