package rebelsky.exam2;

import java.math.BigInteger;

/**
 * Oh boy!  Fun with Fibonacci numbers.
 *
 * @author Samuel A. Rebelsky
 * @version 1.0 of October 2004
 */
public class Fib
{
	/**
	 * A count of the number of calls made.
	 */
	int calls;

	/**
	 * An array to store the partially computed values.
	 */
	BigInteger[] computed;

	/**
	 * Compute the nth Fibonacci number (inefficiently).
	 */
	public BigInteger badfib(int n)
	{
		++this.calls;
		if (n < 2)
			return BigInteger.valueOf(n);
		else
			return badfib(n-1).add(badfib(n-2));
	} // badfib

	/**
	 * Compute the nth Fibonacci number (efficiently)
	 */
	public BigInteger fib(int n)
	{
		// Make sure the array exists and is suffiently big
		if ((computed == null) || (computed.length <= n)) {
			computed = new BigInteger[n+1];
			computed[0] = BigInteger.valueOf(0);
			computed[1] = BigInteger.valueOf(1);
		}
		// See if the value is already there
		if (computed[n] == null) {
			computed[n] = fib(n-1).add(fib(n-2));
		}
		return computed[n];
	} // fib(int)

	/**
	 * Reset the number of calls made.
	 */
	void resetCalls()
	{
		this.calls = 0;
	} // resetCalls()

	/**
	 * Get the number of calls made.
	 */
	int getCalls()
	{
		return this.calls;
	} // getCalls()
} // class Fib