Selecting A Set Of Numbers From A List Which Add Up To A Given Value

How can I choose some numbers from a given list so that their sum is a certain given number? Example: wanted_num = 10 my_list = [1, 3, 11, 123, 5, 4] => [1, 5, 4]

Solution 1:

This is one possible way to do it:

def find_combinations(list, sum):
    ifnot list:
        if sum == 0:
            return[[]]return []
    return find_combinations(list[1:], sum) + \
        [[list[0]] + tail for tail in
         find_combinations(list[1:], sum - list[0])]

For your example, this would return:

>>> print find_combinations([1, 3, 11, 123, 5, 4], 10)
[[1, 5, 4]]

Solution 2:

Here's a more generic version that checks for more than just pairs (basically, any n-tuples that add up to the required target)

deffindSum(target, L, sofar=None):
    if sofar isNone:
        sofar = []
    ifnot target:
        print(sofar)
        returnif target < 0:
        returnfor i,num inenumerate(L):
        findSum(target-num, L[:i]+L[i+1:], sofar+[num])

Output:

In[34]: findSum(10, [1,3,11,123,5,7])
[3, 7][7, 3]

Note that it doesn't exclude similar sets

Solution 3:

The solution below should work:

wanted_num = 10
my_list = [1, 3, 11, 123, 5, 7]
for i in range(0, len(my_list)):
    for j in range(0, len(my_list)):
        if i + j == wanted_num:
            answer = [i, j]
            breakprint(answer)

This solution assumes there's only two numbers that add up to wanted_num. Hope it helps.