/
DoublyLinkedList.java
268 lines (213 loc) · 6.29 KB
/
DoublyLinkedList.java
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/**
* A doubly linked list implementation.
*
* @author William Fiset, william.alexandre.fiset@gmail.com
*/
package com.williamfiset.datastructures.linkedlist;
public class DoublyLinkedList<T> implements Iterable<T> {
private int size = 0;
private Node<T> head = null;
private Node<T> tail = null;
// Internal node class to represent data
private class Node<T> {
T data;
Node<T> prev, next;
public Node(T data, Node<T> prev, Node<T> next) {
this.data = data;
this.prev = prev;
this.next = next;
}
@Override
public String toString() {
return data.toString();
}
}
// Empty this linked list, O(n)
public void clear() {
Node<T> trav = head;
while (trav != null) {
Node<T> next = trav.next;
trav.prev = trav.next = null;
trav.data = null;
trav = next;
}
head = tail = trav = null;
size = 0;
}
// Return the size of this linked list
public int size() {
return size;
}
// Is this linked list empty?
public boolean isEmpty() {
return size() == 0;
}
// Add an element to the tail of the linked list, O(1)
public void add(T elem) {
addLast(elem);
}
// Add a node to the tail of the linked list, O(1)
public void addLast(T elem) {
// The linked list is empty
if (isEmpty()) {
head = tail = new Node<T>(elem, null, null);
} else {
tail.next = new Node<T>(elem, tail, null);
tail = tail.next;
}
size++;
}
// Add an element to the beginning of this linked list, O(1)
public void addFirst(T elem) {
// The linked list is empty
if (isEmpty()) {
head = tail = new Node<T>(elem, null, null);
} else {
head.prev = new Node<T>(elem, null, head);
head = head.prev;
}
size++;
}
// Check the value of the first node if it exists, O(1)
public T peekFirst() {
if (isEmpty()) throw new RuntimeException("Empty list");
return head.data;
}
// Check the value of the last node if it exists, O(1)
public T peekLast() {
if (isEmpty()) throw new RuntimeException("Empty list");
return tail.data;
}
// Remove the first value at the head of the linked list, O(1)
public T removeFirst() {
// Can't remove data from an empty list -_-
if (isEmpty()) throw new RuntimeException("Empty list");
// Extract the data at the head and move
// the head pointer forwards one node
T data = head.data;
head = head.next;
--size;
// If the list is empty set the tail to null
if (isEmpty()) tail = null;
// Do a memory cleanup of the previous node
else head.prev = null;
// Return the data that was at the first node we just removed
return data;
}
// Remove the last value at the tail of the linked list, O(1)
public T removeLast() {
// Can't remove data from an empty list -_-
if (isEmpty()) throw new RuntimeException("Empty list");
// Extract the data at the tail and move
// the tail pointer backwards one node
T data = tail.data;
tail = tail.prev;
--size;
// If the list is now empty set the head to null
if (isEmpty()) head = null;
// Do a memory clean of the node that was just removed
else tail.next = null;
// Return the data that was in the last node we just removed
return data;
}
// Remove an arbitrary node from the linked list, O(1)
private T remove(Node<T> node) {
// If the node to remove is somewhere either at the
// head or the tail handle those independently
if (node.prev == null) return removeFirst();
if (node.next == null) return removeLast();
// Make the pointers of adjacent nodes skip over 'node'
node.next.prev = node.prev;
node.prev.next = node.next;
// Temporarily store the data we want to return
T data = node.data;
// Memory cleanup
node.data = null;
node = node.prev = node.next = null;
--size;
// Return the data in the node we just removed
return data;
}
// Remove a node at a particular index, O(n)
public T removeAt(int index) {
// Make sure the index provided is valid -_-
if (index < 0 || index >= size) throw new IllegalArgumentException();
int i;
Node<T> trav;
// Search from the front of the list
if (index < size / 2) {
for (i = 0, trav = head; i != index; i++) trav = trav.next;
// Search from the back of the list
} else for (i = size - 1, trav = tail; i != index; i--) trav = trav.prev;
return remove(trav);
}
// Remove a particular value in the linked list, O(n)
public boolean remove(Object obj) {
Node<T> trav = head;
// Support searching for null
if (obj == null) {
for (trav = head; trav != null; trav = trav.next) {
if (trav.data == null) {
remove(trav);
return true;
}
}
// Search for non null object
} else {
for (trav = head; trav != null; trav = trav.next) {
if (obj.equals(trav.data)) {
remove(trav);
return true;
}
}
}
return false;
}
// Find the index of a particular value in the linked list, O(n)
public int indexOf(Object obj) {
int index = 0;
Node<T> trav = head;
// Support searching for null
if (obj == null) {
for (; trav != null; trav = trav.next, index++) if (trav.data == null) return index;
// Search for non null object
} else for (; trav != null; trav = trav.next, index++) if (obj.equals(trav.data)) return index;
return -1;
}
// Check is a value is contained within the linked list
public boolean contains(Object obj) {
return indexOf(obj) != -1;
}
@Override
public java.util.Iterator<T> iterator() {
return new java.util.Iterator<T>() {
private Node<T> trav = head;
@Override
public boolean hasNext() {
return trav != null;
}
@Override
public T next() {
T data = trav.data;
trav = trav.next;
return data;
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
};
}
@Override
public String toString() {
StringBuilder sb = new StringBuilder();
sb.append("[ ");
Node<T> trav = head;
while (trav != null) {
sb.append(trav.data + ", ");
trav = trav.next;
}
sb.append(" ]");
return sb.toString();
}
}