/
ArrayDeque.java
150 lines (135 loc) · 3.22 KB
/
ArrayDeque.java
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package com.alexvolov.ads.ds.impl;
import com.alexvolov.ads.ds.Deque;
/**
* An implementation of the deque data structure which is
* based on array and doesn't support resizing.
*
* @author Alexander Volov (mailto: alevolov@gmail.com)
* @version 24.01.15
*/
public class ArrayDeque<T> implements Deque<T> {
private T[] deque;
private int frontIndex, backIndex;
/**
* Constructor.
*
* @param capacity max number of the elements in deque.
*/
@SuppressWarnings("unchecked")
public ArrayDeque(int capacity) {
if (capacity > 0) {
deque = (T[]) new Object[capacity];
frontIndex = -1;
backIndex = -1;
} else {
throw new IllegalArgumentException("Capacity must be greater than zero.");
}
}
/**
* {@inheritDoc}
*/
@Override
public void pushBack(T item) {
if (decrement(backIndex) != frontIndex) {
backIndex = decrement(backIndex);
deque[backIndex] = item;
if (frontIndex == -1) {
frontIndex = backIndex;
}
} else {
throw new RuntimeException("Deque is full.");
}
}
/**
* {@inheritDoc}
*/
@Override
public T popBack() {
T result = null;
if (backIndex != -1) {
result = deque[backIndex];
if (backIndex == frontIndex) {
frontIndex = backIndex = -1;
} else {
backIndex = increment(backIndex);
}
}
return result;
}
/**
* {@inheritDoc}
*/
@Override
public void pushFront(T item) {
if (increment(frontIndex) != backIndex) {
frontIndex = increment(frontIndex);
deque[frontIndex] = item;
if (backIndex == -1) {
backIndex = frontIndex;
}
} else {
throw new RuntimeException("Deque is full.");
}
}
/**
* {@inheritDoc}
*/
@Override
public T popFront() {
T result = null;
if (frontIndex != -1) {
result = deque[frontIndex];
if (frontIndex == backIndex) {
frontIndex = backIndex = -1;
} else {
frontIndex = decrement(frontIndex);
}
}
return result;
}
/**
* {@inheritDoc}
*/
@Override
public boolean isEmpty() {
return frontIndex == -1;
}
/**
* {@inheritDoc}
*/
@Override
public T peekFront() {
T result = null;
if (frontIndex != -1) {
return deque[frontIndex];
}
return result;
}
/**
* {@inheritDoc}
*/
@Override
public T peekBack() {
T result = null;
if (backIndex != -1) {
return deque[backIndex];
}
return result;
}
private int increment(int value) {
if (value + 1 >= deque.length) {
value = 0;
} else {
value++;
}
return value;
}
private int decrement(int value) {
if (value - 1 <= -1) {
value = deque.length - 1;
} else {
value--;
}
return value;
}
}