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  1. import java.util.Scanner;
  2.  
  3. class Deque {
  4.  
  5.     private class Node {
  6.         Node prev;
  7.         Node next;
  8.         int x;
  9.  
  10.         Node() {
  11.             prev = null;
  12.             next = null;
  13.             x = 0;
  14.         }
  15.  
  16.         Node(Node a, Node b, int c) {
  17.             prev = a;
  18.             next = b;
  19.             x = c;
  20.         }
  21.     }
  22.  
  23.     ;
  24.  
  25.     Node Front = null;
  26.     Node Back = null;
  27.     int Size = 0;
  28.  
  29.     int size() {
  30.         return Size;
  31.     }
  32.  
  33.     void push_back(int p) {
  34.         if (Size == 0) {
  35.             Node NewNode = new Node(Back, Front, p);
  36.             Front = NewNode;
  37.             Back = NewNode;
  38.         } else {
  39.             Node NewNode = new Node(null, Back, p);
  40.             Back.prev = NewNode;
  41.             Back = NewNode;
  42.         }
  43.         Size++;
  44.     }
  45.  
  46.     void push_front(int p) {
  47.         if (Size == 0) {
  48.             Node NewNode = new Node(Back, Front, p);
  49.             Front = NewNode;
  50.             Back = NewNode;
  51.         } else {
  52.             Node NewNode = new Node(Front, null, p);
  53.             Front.next = NewNode;
  54.             Front = NewNode;
  55.         }
  56.         Size++;
  57.     }
  58.  
  59.     int back() {
  60.         if (Size != 0) {
  61.             return Back.x;
  62.         } else {
  63.             return 0;
  64.         }
  65.     }
  66.  
  67.     int front() {
  68.         if (Size != 0) {
  69.             return Front.x;
  70.         } else {
  71.             return 0;
  72.         }
  73.     }
  74.  
  75.     int pop_front() {
  76.         if (Size != 0) {
  77.             int x = Front.x;
  78.             Node NewNode = Front.prev;
  79.             Front = NewNode;
  80.             Size--;
  81.             return x;
  82.         } else {
  83.             return 0;
  84.         }
  85.     }
  86.  
  87.     int pop_back() {
  88.         if (Size != 0) {
  89.             int x = Back.x;
  90.             Node NewNode = Back.next;
  91.             Back = NewNode;
  92.             Size--;
  93.             return x;
  94.         } else {
  95.             return 0;
  96.         }
  97.     }
  98.  
  99.     void clear() {
  100.         while (Size > 0) {
  101.             Node NewNode = Front.prev;
  102.             Front = NewNode;
  103.             Size--;
  104.         }
  105.         Front = null;
  106.         Back = null;
  107.     }
  108.  
  109.  
  110.     public static void main(String[] args) {
  111.         Deque deque = new Deque();
  112.         Scanner scanner = new Scanner(System.in);
  113.         System.out.println("enter your command");
  114.         String command = scanner.nextLine();
  115.  
  116.         while (!command.equals("exit")) {
  117.             if (command.equals("push_back")) {
  118.                 int v = scanner.nextInt();
  119.                 deque.push_back(v);
  120.                 System.out.println("ok\n");
  121.             } else if (command.equals("push_front")) {
  122.                 int v = scanner.nextInt();
  123.                 deque.push_front(v);
  124.                 System.out.println("ok\n");
  125.             } else if (command.equals("front")) {
  126.                 if (deque.size() > 0) {
  127.                     System.out.println(deque.front());
  128.                 } else {
  129.                     System.out.println("error\n");
  130.                 }
  131.             } else if (command.equals("back")) {
  132.                 if (deque.size() > 0) {
  133.                     System.out.println(deque.back());
  134.                 } else {
  135.                     System.out.println("error\n");
  136.                 }
  137.             } else if (command.equals("size")) {
  138.                 System.out.println(deque.size());
  139.             } else if (command.equals("pop_front")) {
  140.                 if (deque.size() > 0) {
  141.                     System.out.println(deque.pop_front());
  142.                 } else {
  143.                     System.out.println("error\n");
  144.                 }
  145.             } else if (command.equals("pop_back")) {
  146.                 if (deque.size() > 0) {
  147.                     System.out.println(deque.pop_back());
  148.                 } else {
  149.                     System.out.println("error\n");
  150.                 }
  151.             } else if (command.equals("clear")) {
  152.                 System.out.println("ok\n");
  153.                 deque.clear();
  154.             }
  155.             command = scanner.nextLine();
  156.         }
  157.         System.out.println("bye");
  158.     }
  159. };
Success #stdin #stdout 0.06s 321344KB
comments (?)
stdin
copy 
push_front
4
push_back
5
front
push_front
3
back
size
pop_front
pop_back
clear
pop_back
size
exit
stdout
copy 
enter your command
ok

ok

4
ok

5
3
3
5
ok

error

0
bye
https://ideone.com/ViRNvi
language:
Java (12.0.1)
created:
7 years ago
visibility:
public

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