public class Fibonacci { 
    /* Computes the nth Fibonacci number using its definition */
    static long recFib(int n) {
        return (n < 2) ? n : recFib(n-1) + recFib(n-2);
    }

    /////////////////////////////////////////////////////////////////////////////
    static long[] dpTable;

    /* Computes the nth Fibonacci number using bottom-up dynamic programming. */
    static long dpFib(int n) {
        dpTable[0] = 0;
        if (n > 0)
            dpTable[1] = 1;
        for (int i = 2; i <= n; i++)
            dpTable[i] = dpTable[i-1] + dpTable[i-2];
        return dpTable[n];
    }

    /* Computes the nth Fibonacci number using bottom-up dynamic programming,
     * space-saving.
     */
    static long dpSpaceFib(int n) {
        if (n < 2) return n;

        long prev = 0;
        long curr = 1;
        for (int i = 2; i <= n; i++) {
            curr = curr + prev;
            prev = curr - prev;
        }
        return curr;
    }

    /////////////////////////////////////////////////////////////////////////////
    static long[] mzTable;
    static final long UNKNOWN = -1;

    static long memoize(int n) {
        if (mzTable[n] == UNKNOWN)
            mzTable[n] = (n < 2) ? n : memoize(n-1) + memoize(n-2);
        return mzTable[n];
    }

    /* Computes the nth Fibonacci number using memoization (a top-down approach). */
    static long mzFib(int n) {
        /* initialize mzTable */
        for (int i = 0; i < mzTable.length; i++)
            mzTable[i] = UNKNOWN;

        return memoize(n);
    }

    /////////////////////////////////////////////////////////////////////////////
    public static void main(String[] args) { 
        int n = Integer.parseInt(args[0]);

        if (n < 0) {
            System.err.println("argument must be a nonnegative integer");
            System.exit(1);
        }

        long value;
        double time;

        Stopwatch sw1 = new Stopwatch();
        value = recFib(n);
        time = sw1.elapsedTime();
        System.out.printf("%nrecFib(%d) = %d%n", n, value);
        System.out.printf("time spent: %.2f%n", time);

        mzTable = new long[n+1];
        Stopwatch sw2 = new Stopwatch();
        value = mzFib(n);
        time = sw2.elapsedTime();
        System.out.printf("%nmzFib(%d) = %d%n", n, value);
        System.out.printf("time spent: %.2f%n", time);

        dpTable = new long[n+1];
        Stopwatch sw3 = new Stopwatch();
        value = dpFib(n);
        time = sw3.elapsedTime();
        System.out.printf("%ndpFib(%d) = %d%n", n, value);
        System.out.printf("time spent: %.2f%n", time);

        Stopwatch sw4 = new Stopwatch();
        value = dpSpaceFib(n);
        time = sw4.elapsedTime();
        System.out.printf("%ndpSpaceFib(%d) = %d%n", n, value);
        System.out.printf("time spent: %.2f%n%n", time);
    }
}