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CircularQueue.java

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import java.util.NoSuchElementException;

class CircularQueue {

private String[] queue;

private int n;

private int first;

private int last;

public CircularQueue() {

queue = new String[2];

n = 0;

first = 0;

last = 0;

}

public boolean isEmpty() {

return n == 0;

}

public int size() {

return n;

}

private void resize(int capacity) {

String[] copy = new String[capacity];

for (int i = 0; i < n; ++i) {

copy[i] = queue[(first + i) % queue.length];

}

queue = copy;

first = 0;

last = n;

}

public void enqueue(String s) {

if (n == queue.length) {

resize(2 * queue.length);

}

queue[last++] = s;

if (last == queue.length) {

last = 0;

}

n++;

}

public String dequeue() {

if(isEmpty()) {

throw new NoSuchElementException("Underflow");

}

String s = queue[first];

queue[first] = null;

first++;

n--;

if (first == queue.length) {

first = 0;

}

if (n > 0 && n == queue.length / 4) {

resize(queue.length / 2);

}

return s;

}

public static void main(String[] args) {

String[] string = {"a", "b", "c", "d", "e"};

CircularQueue queue = new CircularQueue();

System.out.println("Size : " + queue.size() + ", isEmpty: " + queue.isEmpty());

for (String s : string) {

queue.enqueue(s);

System.out.println("Size : " + queue.size() + ", isEmpty: " + queue.isEmpty());

}

while (!queue.isEmpty()) {

System.out.println("Deuque : " + queue.dequeue());

System.out.println("Size : " + queue.size() + ", isEmpty: " + queue.isEmpty());

}

System.out.println("Size : " + queue.size() + ", isEmpty: " + queue.isEmpty());

}