记忆使用/缓存存储

Question

I am writing a program that calculates the Pascal Identity of two variables, hard coded into the program, as I am new into Python and trying out caching and memoization. Here is what I have so far:

counter = 0

call_cacheK = {}
   def callTest(n, k):
   global counter

   if n in call_cacheK:
       return call_cacheK[n]  
   if k == 0:
       return 1
   elif k == n:
       return 1 
   elif (1 <= k) and (k <= (n-1)):
       counter += 1
       #call_cacheK[n] = result
       result = ((callTest(n-1, k) + callTest(n-1, k-1)))
   print(result)
   return result

callTest(20, 11)
#167,960

My function will output the final real answer with what it has now, but with a lot of outputted answers. I cannot seem to get how to properly store the values to be used in the cache.

How do I properly use call_cacheK to store the result values I have already used?

Thank you.

Answer 1

Lets see. First, you have a function of two variables, but store result in cache only by one parameter. So callTest(20, 11) , callTest(20, 10) , callTest(20, 9) will have one result in your cache. Lets rewrite your function a little:

call_cacheK = {}

def callTest(n, k):
    if (n, k) in call_cacheK:
        return call_cacheK[(n, k)]  
    if k == 0:
        return 1
    elif k == n:
        return 1 
    elif (1 <= k) and (k <= (n-1)):
        result = ((callTest(n-1, k) + callTest(n-1, k-1)))
        call_cacheK[(n, k)] = result
    print(result)
    return result

Yes there is no counter variable because I didn't realize why do you need it :)

Also, as far as I can judge by the use of print(result) , you probably use the Python3.x. If so, you can use standard cache implementing :

from functools import lru_cache

@lru_cache(maxsize=None)
def callTest2(n, k):  
    if k == 0:
        return 1
    elif k == n:
        return 1 
    elif (1 <= k) and (k <= (n-1)):
        result = ((callTest2(n-1, k) + callTest2(n-1, k-1)))
    print(result)
    return result

Good luck! :)