Python function to add numbers from string

Question

I was recently given this problem and tasked with coding a solution. My efforts so far have come close but not yet solved it.

Essentially, the problem involves creating a function which is passed a string of numbers (no validation required), for example '12345'.

I have to code the function (using Python preferably) that adds all the consecutive combination of digits. For the above example, this would be:

12345 + 1 + 2 + 3 + 4 + 5
+ 12 + 23 + 34 + 45
+ 123 + 234 + 345
+ 1234 + 2345

I have got some things working, for example:

#code to add the individual numbers
indivInts = [int(d) for d in stringNumber]
for i in indivInts:
        total += i

#code to add 12 + 123 + 12345, etc
for i in range(len(stringNumber)-2):
        s = ''.join([str(x) for x in indivInts[:i+2]])
        print('Adding loop 2: ' + s)
        total += int(s)

The issue I seem to be having is with the 'middle' numbers, ie 234, 34, etc.

The function should be able to take any string of an integer and still work.

Just to make sure: Should the first number in the sequence relaly be 123456 or 12345? — tobias_k
– tobias_k, Commented Sep 2, 2019 at 15:38
Apologies, updated the Q now! taken out the 123456 - thanks Tobias — nimgwfc
– nimgwfc, Commented Sep 2, 2019 at 15:40

tobias_k · Accepted Answer · 2019-09-02 15:42:45Z

4

Basically you need the list of all possible substrings of the original number. You can use a list comprehension with two loops for the lower and upper bounds for this.

>>> s = "12345"
>>> [s[i:k+1] for i in range(0, len(s)) for k in range(i, len(s))]
['1', '12', '123', '1234', '12345', '2', '23', '234', '2345', '3', '34', '345', '4', '45', '5']

Then just get the sum of the previously generated list, converted to int:

>>> sum(map(int, _))
16755

In a single line:

>>> sum(int(s[i:k+1]) for i in range(0, len(s)) for k in range(i, len(s)))
16755

Or as a regular nested loop:

s = "12345"
r = 0
for i in range(0, len(s)):
    for k in range(i, len(s)):
        r += int(s[i:k+1])
print(r)

edited Sep 2, 2019 at 15:42

answered Sep 2, 2019 at 15:30

tobias_k

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3 Comments

Flo Over a year ago

Nice code, +1. By the way you're missing "123456" (aka original number) in the sum :)

tobias_k Over a year ago

@Flo Whops, messed up my upper bound. Give me a second... Okay, should be fixed now.

nimgwfc Over a year ago

This is much better than what I had been trying... thanks!

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