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ArrayDeque.java
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ArrayDeque.java
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package comp2402a2;
import java.util.AbstractList;
/**
* An implementation of the List interface that allows for fast modifications
* at both the head and tail.
*
* The implementation is as a circular array. The List item of rank i is stored
* at a[(j+i)%a.length]. Insertions and removals at position i take
* O(1+min{i, size()-i}) amortized time.
* @author morin
*
* @param <T> the type of objects stored in this list
* TODO: Implement addAll() and removeAll() efficiently
*/
public class ArrayDeque<T> extends AbstractList<T> {
/**
* The class of elements stored in this queue
*/
protected Factory<T> f;
/**
* Array used to store elements
*/
protected T[] a;
/**
* Index of next element to de-queue
*/
protected int j;
/**
* Number of elements in the queue
*/
protected int n;
/**
* Grow the internal array
*/
protected void resize() {
T[] b = f.newArray(Math.max(2*n,1));
for (int k = 0; k < n; k++)
b[k] = a[(j+k) % a.length];
a = b;
j = 0;
}
/**
* Constructor
*/
public ArrayDeque(Class<T> t) {
f = new Factory<T>(t);
a = f.newArray(1);
j = 0;
n = 0;
}
public int size() {
return n;
}
public T get(int i) {
if (i < 0 || i > n-1) throw new IndexOutOfBoundsException();
return a[(j+i)%a.length];
}
public T set(int i, T x) {
if (i < 0 || i > n-1) throw new IndexOutOfBoundsException();
T y = a[(j+i)%a.length];
a[(j+i)%a.length] = x;
return y;
}
public void add(int i, T x) {
if (i < 0 || i > n) throw new IndexOutOfBoundsException();
if (n+1 > a.length) resize();
if (i < n/2) { // shift a[0],..,a[i-1] left one position
j = (j == 0) ? a.length - 1 : j - 1; // (j-1) mod a.length
for (int k = 0; k <= i-1; k++)
a[(j+k)%a.length] = a[(j+k+1)%a.length];
} else { // shift a[i],..,a[n-1] right one position
for (int k = n; k > i; k--)
a[(j+k)%a.length] = a[(j+k-1)%a.length];
}
a[(j+i)%a.length] = x;
n++;
}
public T remove(int i) {
if (i < 0 || i > n - 1) throw new IndexOutOfBoundsException();
T x = a[(j+i)%a.length];
if (i < n/2) { // shift a[0],..,[i-1] right one position
for (int k = i; k > 0; k--)
a[(j+k)%a.length] = a[(j+k-1)%a.length];
j = (j + 1) % a.length;
} else { // shift a[i+1],..,a[n-1] left one position
for (int k = i; k < n-1; k++)
a[(j+k)%a.length] = a[(j+k+1)%a.length];
}
n--;
if (3*n < a.length) resize();
return x;
}
public void clear() {
n = 0;
resize();
}
}