Solution:
The time complexity of iterator() is O(N), the other methods are O(1). The space complexity is O(N).
import java.util.Iterator;
public class MyCollection<Item> implements Iterable<Item> {
private Node first;
private class Node {
Item item;
Node next;
}
private int N = 0;
public boolean isEmpty() {return N == 0;}
public int size() {return N;}
public void add(Item item) {
Node oldfirst = first;
first = new Node();
first.item = item;
first.next = oldfirst;
N++;
}
@Override
public Iterator<Item> iterator() {
return new MyIterator();
}
private class MyIterator implements Iterator<Item> {
Node current = first;
@Override
public boolean hasNext() {
return current != null;
}
@Override
public Item next() {
Item item = current.item;
current = current.next;
return item;
}
}
public static void main(String...args) {
MyCollection<Integer> c = new MyCollection<>();
c.add(1);
c.add(3);
c.add(6);
System.out.println(c.size());
Iterator<Integer> it = c.iterator();
System.out.println(c.isEmpty());
System.out.println();
while(it.hasNext()) {
System.out.print(it.next() + " ");
}
System.out.println();
}
}
