Another example of memoization with Clojure, also using Fibonacci

memoization2.clj

; without memoization

(defn fib [n]
  (if  (or (zero? n) (= n 1)) 
    1 
    (+  (fib (dec n) )  (fib (- n 2)))))

(time (fib 90))
; spent more than 30 minutes and I quit

; I don't know if it sounds right, but worked fine

(def fib-memo)

(defn fib [n]
  (if  (or (zero? n) (= n 1)) 
    1 
    (+  (fib-memo (dec n) )  (fib-memo (- n 2))))) 

(def fib-memo (memoize fib))

(time (fib 90))
; "Elapsed time: 0.058 msecs"
; 4660046610375530309