Dequeue

Deque

A “Double-Ended Queue” (Deque) is a collection of items where elements can be added or removed from both the front and back — combining features of both stacks and queues.

• Data structures
  • Linkedlist - doubly linked list

Code

public static void main(String[] args) {
 
    Deque<Integer> deque = new ArrayDeque<>();
 
    // Deque에 데이터 추가
    deque.addFirst(1);     // 앞쪽에 추가
    deque.addLast(2);      // 뒤쪽에 추가
    deque.addFirst(0);     // 다시 앞쪽에 추가
 
    System.out.println(deque);
 
    // 데이터 조회
    System.out.println("peekFirst() : " + deque.peekFirst()); // 0
    System.out.println("peekLast() : " + deque.peekLast());   // 2
 
    // 데이터 제거
    System.out.println("removeFirst() : " + deque.removeFirst()); // 0 제거
    System.out.println("removeLast() : " + deque.removeLast());   // 2 제거
 
    System.out.println(deque);
}

Using it like a stack/queue

public static void main(String[] args) {
 
    Deque<Integer> dequeAsStack = new ArrayDeque<>();
 
    // Stack처럼 사용 (LIFO)
    dequeAsStack.addLast(1);
    dequeAsStack.addLast(2);
    dequeAsStack.addLast(3);
 
    System.out.println(dequeAsStack.removeLast()); // 3
    System.out.println(dequeAsStack.removeLast()); // 2
 
    Deque<Integer> dequeAsQueue = new ArrayDeque<>();
 
    // Queue처럼 사용 (FIFO)
    dequeAsQueue.addLast(1);
    dequeAsQueue.addLast(2);
    dequeAsQueue.addLast(3);
 
    System.out.println(dequeAsQueue.removeFirst()); // 1
    System.out.println(dequeAsQueue.removeFirst()); // 2
}