package com.thealgorithms.datastructures.lists;
public class CircleLinkedList<E> {
private static final class Node<E> {
Node<E> next;
E value;
private Node(E value, Node<E> next) {
this.value = value;
this.next = next;
}
}
// For better O.O design this should be private allows for better black box design
private int size;
// this will point to dummy node;
private Node<E> head = null;
private Node<E> tail = null; // keeping a tail pointer to keep track of the end of list
// constructor for class.. here we will make a dummy node for circly linked list implementation
// with reduced error catching as our list will never be empty;
public CircleLinkedList() {
// creation of the dummy node
head = new Node<E>(null, head);
tail = head;
size = 0;
}
// getter for the size... needed because size is private.
public int getSize() {
return size;
}
// for the sake of simplistiy this class will only contain the append function or addLast other
// add functions can be implemented however this is the basses of them all really.
public void append(E value) {
if (value == null) {
// we do not want to add null elements to the list.
throw new NullPointerException("Cannot add null element to the list");
}
// head.next points to the last element;
if (tail == null) {
tail = new Node<E>(value, head);
head.next = tail;
} else {
tail.next = new Node<E>(value, head);
tail = tail.next;
}
size++;
}
public String toString() {
if (size == 0) {
return "[]";
}
StringBuilder sb = new StringBuilder("[ ");
Node<E> current = head.next;
while (current != head) {
sb.append(current.value);
if (current.next != head) {
sb.append(", ");
}
current = current.next;
}
sb.append(" ]");
return sb.toString();
}
public E remove(int pos) {
if (pos >= size || pos < 0) {
// catching errors
throw new IndexOutOfBoundsException("position cannot be greater than size or negative");
}
// we need to keep track of the element before the element we want to remove we can see why
// bellow.
Node<E> before = head;
for (int i = 1; i <= pos; i++) {
before = before.next;
}
Node<E> destroy = before.next;
E saved = destroy.value;
// assigning the next reference to the element following the element we want to remove...
// the last element will be assigned to the head.
before.next = before.next.next;
// scrubbing
if (destroy == tail) {
tail = before;
}
destroy = null;
size--;
return saved;
}
}