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LinkedListQueue.java
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LinkedListQueue.java
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package com.faisal;
import java.util.ArrayList;
public class LinkedListQueue {
private class Node {
private int value;
private Node next;
public Node(int value) {
this.value = value;
}
}
private Node head;
private Node tail;
private int count;
// O(1)
public void enqueue(int item) {
var node = new Node(item);
if (isEmpty())
head = tail = node;
else {
tail.next = node;
tail = node;
}
count++;
}
// O(1)
public int dequeue() {
if (isEmpty())
throw new IllegalStateException();
int value;
if (head == tail) {
value = head.value;
head = tail = null;
} else {
value = head.value;
var second = head.next;
head.next = null;
head = second;
}
count--;
return value;
}
// O(1)
public int peek() {
if (isEmpty())
throw new IllegalStateException();
return head.value;
}
// O(1)
public int size() {
return count;
}
// O(1)
public boolean isEmpty() {
return head == null;
}
// O(n)
public String toString() {
ArrayList<Integer> list = new ArrayList<>();
Node current = head;
while (current != null) {
list.add(current.value);
current = current.next;
}
return list.toString();
}
}