我需要一些帮助，将字典用作 function 参数

Question

I need to replicate this same function but instead of having a list as a parameter I need a dictionary. The idea is that the calculation done by the function is done with the values, and the function returns the keys.

def funcion(dic, Sum):
    
    Subset = []
    
    def f(dic, i, Sum):
        if i >= len(dic): return 1 if Sum == 0 else 0
        count = f(dic, i + 1, Sum)
        count += f(dic, i + 1, Sum - dic[i])
        return count

    for i, x in enumerate(dic):
        if f(dic, i + 1, Sum - x) > 0:
            Subset.append(x)
            Sum -= x
    return Subset

The function works if I enter (300, 200,100,400). But i need to use as an input something like {1:300, 2:200, 3:100, 4:400 } So the calculation is done with the values, but it returns the keys that match the condition.

Im trying working with dic.keys() and dic.values() but its not working. Could you help me?

Thank u so much.

Answer 1

Your code isn't working with your dictionary because it's expecting to be able to index into dic with numeric indexes starting at 0 and going up to len(dic)-1 . However, you've given your dictionary keys that start at 1 and go to len(dic) . That means you need to change things up.

The first change is in the recursive f function, where you need the base case to trigger on i > len(dic) rather than using the >= comparison.

The next change in in the loop that calls f . Rather than using enumerate , which will generate indexes starting at 0 (and pair them with the keys of the dictionary, which is what you get when you directly iterate on it), you probably want to do something else.

Now, ideally, you'd want to iterate on dic.items() , which would give you index, value pairs just like your code expects. But depending on how the dictionary gets built, that might iterate over the values in a different order than you expect. In recent versions of Python, dictionaries maintain the order their keys were added in, so if you're creating the dictionary with {1:300, 2:200, 3:100, 4:400 } , you'll get the right order, but a mostly-equivalent dictionary like {3:100, 4:400, 1:300, 2:200 } would give its results in a different order.

So if you need to be resilient against dictionaries that don't have their keys in the right order, you probably want to directly generate the 1 - len(dict) keys yourself with range , and then index to get the x value inside the loop:

for i in range(1, len(dic)+1):      # Generate the keys directly from a range
    x = dic[i]                      # and do the indexing manually.
    if f(dic, i + 1, Sum - x) > 0:  # The rest of the loop is the same as before.
        Subset.append(x)
        Sum -= x