package rebelsky.exam2.solutions;

/**
 * Something that helps us count coints.
 *
 * @author Samuel A. Rebelsky
 * @author CSC152 2004F
 */
public class CoinCounter
{
// +--------+--------------------------------------------------
// | Fields |
// +--------+

	/** 
	 * The valid coin values.
	 */
	int[] denominations;

	/**
	 * The number of recursive calls.
	 */
	int calls;

	/**
	 * Yay!  Stuff to make us more efficient.
	 */
	int cache[];


// +--------------+--------------------------------------------
// | Constructors |
// +--------------+

	/**
	 * Build a new coin counter for a particular set of denominations.
	 *
	 * @pre
	 *   The values in _denominations must be stored in 
	 *   decreasing order.
	 * @pre
	 *   All values in _denominations must be positive.
	 */
	public CoinCounter(int[] _denominations)
	{
		this.denominations = _denominations;
	} // CoinCounter(int[])


// +----------------+------------------------------------------
// | Public Methods |
// +----------------+

	/**
	 * Determine the fewest number of coins necessary to
	 * make a particular price.
	 *
	 * @exception Exception
	 *   If it is not possible to make that price.
	 */
	public int fewestCoins(int price)
		throws Exception
	{
		++this.calls;

		// Simple solution: No coins needed for no price.
		if (price == 0)
			return 0;

		// Make sure the cache is big enough.
		if ((cache == null) ||  (cache.length <= price)) {
			cache = new int[price+1];
		}

		// Check the cache.
		if (cache[price] != 0) {
			if (cache[price] == Integer.MAX_VALUE)
				throw new Exception("");
			else
				return cache[price];
		}

		// Fewest represents the fewest coins we've done so far
		int fewest = Integer.MAX_VALUE;
		for (int i = 0; i < this.denominations.length; i++) {
			int coin = this.denominations[i];
			if (coin <= price) {
				try {
					int sub = this.fewestCoins(price-coin);
					if (sub+1 < fewest)
						fewest = sub+1;
				} // try
				catch (Exception e) {
					// It's okay we failed, we'll just
					// try a different denomination.
				} // catch
			} // if (coin <= price)
		} // for

		// Update the cache
		cache[price] = fewest;

		// Make sure that we found a solution
		if (fewest == Integer.MAX_VALUE)
			throw new Exception("Can't make change for " + price);
		return fewest;
	} // fewestCoins(int)

	/**
	 * Reset the count of number of calls to fewestCoins.
	 */
	public void resetCalls()
	{
		this.calls = 0;
	} // resetCalls()

	/**
	 * Get the count of the number of calls to fewestCoins.
	 */
	public int getCalls()
	{
		return this.calls;
	} // getCalls()

} // class CoinCounter