// A generic Dictionary class which maps keys to values.

import java.util.*;

public class Dictionary<K, V> {

	private ArrayList<Pair<K, V>> entries;

	// Another solution would be to use two ArrayLists, one holding
	// keys and one holding values. However, this solution is
	// cleaner: it makes explicit the fact that the keys and values
	// are associated. With two ArrayLists, the fact that they go
	// together exists only in the mind of the programmer, and we
	// would have to be very careful not to let the two lists get out
	// of sync. For example, inserting a key into the middle of the
	// first list and forgetting to insert a value in the
	// corresponding place in the second list would wreak havoc (all
	// the following keys would suddenly correspond to different
	// values, and the last key wouldn't correspond to any value at
	// all)! With this solution, that can't happen.

	public Dictionary() {
		entries = new ArrayList<Pair<K, V>>();
	}

	public void add(K key, V value) {
		// look for the key and update the value if it already exists.
		for (Pair<K, V> p : entries) {
			if (p.getFirst().equals(key)) {
				p.setSecond(value);
				return;
			}
		}

		// didn't find the key, so add a new pair.
		entries.add(new Pair<K, V>(key, value));
	}

	public V lookup(K key) {

		for (Pair<K, V> p : entries) {
			if (p.getFirst().equals(key)) {
				return p.getSecond();
			}
		}

		// One might wonder whether we could use the indexOf method of
		// ArrayList instead of using an explicit for loop to search
		// the entries list. We could --- but only if we overrode the
		// equals method of Pair to only look at the first component
		// and ignore the second. This is left as an exercise for the
		// reader. =)

		return null;
	}

	public void remove(K key) {
		// Since we want to remove something, we can't use a foreach
		// loop; we have to use an explicit iterator.
		for (Iterator<Pair<K, V>> it = entries.iterator(); it.hasNext();) {
			if (it.next().getFirst().equals(key)) {
				it.remove();
				return;
			}
		}
	}
}