[CareerCup] 14.6 CircularArray 环形数组

14.6 Implement a CircularArray class that supports an array-like data structure which can be efficiently rotated.The class should use a generic type, and should support iteration via the standard for (Obj o : CircularArray) notation.

这道题让我们实现一个环形数组类CircularArray，由于环形数组需要调用rotate(int shiftRight)函数，在这里，我们并不会真的去旋转数组，因为这样十分不高效。我们采用另一种实现方法，用一个变量head来记录环形数组的起始位置，那么调用rotate实际上就是改变head的位置而已。请参见如下代码：

public static class CircularArray<T> implements Iterable<T> {
    private T[] items;
    private int head = 0;
    
    public CircularArray(int size) {
        items = (T[]) new Object[size];
    }
    
    private int convert(int idx) {
        if (idx < 0) {
            idx += items.length;
        }
        return (head + idx) % items.length;
    }
    
    public void rotate(int shiftRight) {
        head = convert(shiftRight);
    }
    
    public T get(int i) {
        if (i < 0 || i >= items.length) {
            throw new java.lang.IndexOutOfBoundsException("...");
        }
        return items[convert(i)];
    }
    
    public void set(int i, T item) {
        items[convert(i)] = item;
    }
    
    public Iterator<T> iterator() {
        return new CircularArrayIterator<T> (this);
    }
    
    private class CircularArrayIterator<TI> implements Iterator<TI> {
        private int _current = -1;
        private TI[] _items;
        
        public CircularArrayIterator(CircularArray<TI> array) {
            _items = array.items;
        }
        
        @Override
        public boolean hasNext() {
            return _current < items.length - 1;
        }
        
        @Override
        public TI next() {
            ++_current;
            TI item = (TI) _items[convert(_current)];
            return item;
        }
        
        @Override
        public void remove() {
            throw new UnsupportedOperationException("...");
        }
    }
}