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New data structure #199

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130 changes: 130 additions & 0 deletions data_structures/Lists/ArrayBasedList.java
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Original file line number Diff line number Diff line change
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public class ArrayBasedList<T>
{
public static final int INITIAL_CAPACITY = 10;
private T[] items; // an array of list items
private int numItems; // number of items in list

public ArrayBasedList()
{
this.items = (T[]) new Object[INITIAL_CAPACITY];
this.numItems = 0;
}

/*
* Internal method for resizing the array and copying the items over
*/
private void resize()
{
// create a temporary array with a size 2 times larger then current array
T[] new_items = (T[]) new Object[this.items.length * 2];

// iterate through current array and add elements to new array
for (int i = 0; i < this.items.length; i++) {
new_items[i] = this.items[i];
}

this.items = new_items;
}

/*
* Determines whether the list if empty
*
* @return True if the list is empty, false otherwise
*/
public boolean isEmpty()
{
return (this.numItems == 0);
}

/*
* Returns the number of items in the list
*
* @return The number of items in the list
*/
public int size()
{
return this.numItems;
}

/*
* Empty the list
*/
public void removeAll()
{
// set items equal to a new array, old one is deleted
this.items = (T[]) new Object[INITIAL_CAPACITY];
this.numItems = 0;
}

/*
* Add an item to the list at specified index
*
* @param index The position to add the item at
* @param item The item to add to the list
*/
public void add(int index, T item)
{
// if we have no more space, resize the array
if (numItems == items.length) {
resize();
}

if (index >= 0 && index <= numItems) {
// move all items greater than or equal to index to the right
// to make room for new item
for (int i = numItems - 1; i >= index; i--) {
items[i + 1] = items[i];
}
// insert new item
items[index] = item;
numItems++;
}
}

/*
* Retrieves an item from the list
*
* @param index The index to retrieve
* @return The item at the specified index
*/
public T get(int index)
{
if (index >= 0 && index < numItems) {
return items[index];
} else {
return null;
}
}

/*
* Remove an item from the list
*
* @param index The position of the item to remove
*/
public void remove(int index)
{
if (index >= 0 && index < numItems) {
// remove item by shifting all items above it down
for (int i = index + 1; i < numItems; i++) {
items[i - 1] = items[i];
}
items[--numItems] = null; // drop a null to fix memory leak
}
}

/*
* Format a string that displays the items in the list
*
* @return A string displaying the list
*/
public String toString()
{
String output = "List of size " + numItems + " has the following items: ";
for (T o : items) {
if (o != null) {
output += o + " ";
}
}
return output;
}
}