gistfile1.java

import java.util.Arrays;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.lang.Iterable;
import java.util.NoSuchElementException;

import javax.naming.OperationNotSupportedException;

/**
 * An iterator that flattens an iterator of iterators.
 *
 * Iterator SQUARED!
 */
public class IteratorIterator<T> implements Iterator<T> {

    private Iterator<Iterable<T>> _outerIterator;
    private Iterator<T> _innerIterator;

    @SafeVarargs
    public <T> IteratorIterator(Iterable<T>... iterables) {
        _outerIterator = Arrays.asList(iterables).iterator();
        _innerIterator = _outerIterator.next().iterator();
    }

    @Override
    public boolean hasNext() {
        if (_innerIterator.hasNext()) {
            return true;
        } else {
            while(_outerIterator.hasNext()) {
                _innerIterator = _outerIterator.next().iterator();
                if (_innerIterator.hasNext()) {
                    return true;
                }
            }
        }
        return false;
    }

    @Override
    public T next() {
        if (_innerIterator.hasNext()) {
            return _innerIterator.next();
        } else {
            while(_outerIterator.hasNext()) {
                _innerIterator = _outerIterator.next().iterator();
                if (_innerIterator.hasNext()) {
                    return _innerIterator.next();
                }
            }
        }
        throw new NoSuchElementException();
    }

    @Override
    public void remove() {
        // Ignore this function
        try {
            throw new OperationNotSupportedException("Don't worry about this one");
        } catch (OperationNotSupportedException e) {
            e.printStackTrace();
        }
    }


    /**
     * The below is meant to be a test case for your implementation above. If done correctly,
     * it should print out the digits from 1 to 10, one per line, without any blank lines.
     */
    public static void main(String... args) {
        List<Integer> a = Arrays.asList(new Integer[] {1 });
        List<Integer> b = Arrays.asList(new Integer[] {2, 3});
        List<Integer> c = Arrays.asList(new Integer[] { });
        List<Integer> d = Arrays.asList(new Integer[] { });
        List<Integer> e = Arrays.asList(new Integer[] {4});
        List<Integer> f = Arrays.asList(new Integer[] { });
        List<Integer> g = Arrays.asList(new Integer[] {5, 6, 7, 8, 9, 10});
        List<Integer> h = Arrays.asList(new Integer[] { });

        IteratorIterator<Integer> it = new IteratorIterator<Integer>(a, b, c, d, e, f, g, h);
        while (it.hasNext()) {
            System.out.println(it.next());
        }


        System.out.println("Done!");
    }
}