Project Euler #13 understandning (Python)

Question

Problem 13: http://projecteuler.net/problem=13

Work out the first ten digits of the sum of the following one-hundred 50-digit numbers. So, is the question sum the 5000 digits and the answer is the first 10 digits in the result?

bignumber = list of the 5000 digits
sum(bignumber) = abcdefghijklmnopqrst...    
answer = abcdefghj

Well when I do this sum(bignumber) = 22660 (which even is not 10 digits)...

have I misread the question?

def foo():
    with open ("bignumber", "r") as myfile:
        data=myfile.read().replace('\n', '')
    data = map(long, data)
    datasum = sum(data)
    return (datasum)

The question is to sum the 100 numbers, not to sum their digits. — Russell Zahniser, Nov 21 '13 at 15:28
Note that the question is a bit easier in python, since integers have no maximum: http://stackoverflow.com/questions/4581842/python-integer-ranges, so you do not have to deal with overflow. — colcarroll, Nov 21 '13 at 15:31
Lets say someone wanted to do this in another language like C#. How could they overcome the limitations of the ulong being only 20 digits max in length? — , Apr 26 '22 at 17:53

Colin D · Accepted Answer · 2014-07-29T14:15:55.383

5

You are misreading the question.

They give you 100 numbers that you need to sum, each of which is 50 digits long (aka magnitude of X*10^50). The 50 digit part is there so you cant just use traditional int/long data types (As JLLAgrange points out, this part shouldn't be a problem for python since integers have no max value).

edited Jul 29 '14 at 14:15

answered Nov 21 '13 at 15:29

Colin D

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Each number is 50 digits long and there are one-hundred numbers of such length. – Roman Dryndik Jul 29 '14 at 13:57

score 0 · Answer 2 · answered Nov 21 '13 at 15:29

0

Each number is 50 digits long (i.e., each line is a digit). You might try

def foo():
    with open ("bignumber", "r") as myfile:
        data=myfile.read()
    data = map(int, data)
    datasum = sum(data)
    return datasum

answered Nov 21 '13 at 15:29

colcarroll

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score 0 · Answer 3 · answered Nov 21 '13 at 15:35

I think you understood the question correctly, but applied wrongly in Python.

You are doing:

with open ("bignumber", "r") as myfile:
    data=myfile.read().replace('\n', '')
    #Now `data` is a big huge string of digits
data = map(long, data)
#Now data is an array of 5000 elements of each digit.
#And then you are trying sum this array of digits.

What you need:

with open(..) as fileObj:
    data = [long(line.strip()) for line in fileObj]

Look at this example

Project Euler #13 understandning (Python)

3 Answers3

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