Question

Common LISP function

Give a trace of the function when the input is 5

(defun guess (N)

(if (or (zerop N) (= N 1)) 1

(+ (guess (- N 1)) (guess (- N 2)))))

I have ran this code and with the following commands and i get this:

> (trace)

>(guess 5)

1. Trace: (GUESS '5)

1. Trace: (GUESS ==> 8

8

Is this correct or am i doing something wrong plz help.

Answer 1

Solution:

Let's do the trace here,

so N= 5

will call

guess(5)

initial condition if (or (zerop N) (= N 1)) will fail

and

(+ (guess (4)) (guess (3))))) => (Thi is equivlanet to guess(4) + guess(3))

again

(+ (guess (3)) (guess (2))))) => (Thi is equivlanet to guess(3) + guess(2))

again

(+ (guess (2)) (guess (1))))) => (Thi is equivlanet to guess(2) + guess(1))

here guess(1) will return 1

and guess(2) will be called

(+ (guess (1)) (guess (0))))) => (Thi is equivlanet to guess(1) + guess(0))

both the calls will return 1 and guess(2) will return 2

Now, let's get back

==============================================================

now we are returning the values and going backwards

(+ (guess (2)) (guess (1))))) => (Thi is equivlanet to guess(2) + guess(1)) will retun 3 (2+1)

(+ (guess (3)) (guess (2))))) => (Thi is equivlanet to guess(3) + guess(2)) will return 3 + 2 = 5

(+ (guess (4)) (guess (3))))) => (Thi is equivlanet to guess(4) + guess(3)) will return 5+3 = 8

You are absolutely right. :)

I hope this helps if you find any problem. Please comment below. Don't forget to give a thumbs up if you liked it. :)