0

I am writing a function that takes a target sum and an array of numbers as argument. The function should return a boolean ndicating if the target sum can be generated using the numbers from the array. I want to make the program more efficient, but when introducing a dictionary as a third argument, it stores information that are used when I run the function again. Here is the code:

def targetsum(TarS,lis, memo={}):
    if TarS in memo:
        return memo[TarS]
    if TarS==0: return True
    if TarS<0: return False
    for num in lis:
        remainder=TarS-num
        if targetsum(remainder,lis,memo) == True:
            memo[TarS]= True
            return True
    memo[TarS]= False
    return False

print(targetsum(7,[2,4]))  #false
print(targetsum(7,[2,3]))  #true

The program returns false, false because it 'remembers' that 7 gives false from the first run. If I run I comment out one of the 'print' commands, everything works fine. How can I fix it? Thank you!

mathimatikos
  • 3
  • 2
  • Two options: make the default an immutable flag-value, like `None`, or add a nested function to do the recursion and leave out the last argument from the user-facing interface entirely. I would go with the latter option, although in some cases the former could be more flexible. – Mad Physicist Oct 07 '22 at 16:52

0 Answers0