Iterating through a list of string elements in Python, and making that iterator into an int

Question

I have this code, which splits a number into groups of 5, puts them into a list, and then multiples them. This is Problem 8 in Project Euler, if you're confused. It's also not finished, as I need to find the other possible 5 consecutive integers.

def split_number(number, n):

    line = str(number)

    split = [line[i:i+n] for i in range(0, len(line), n)]

    return split

splitnum = split_number((extremely long number), 5)

for x in enumerate(splitnum[:-1]):
    split5 = split_number(splitnum[x], 1)
    for n in split5:
        splitproduct = reduce(lambda x, y: x*y, splitnum[n])
    if (splitproduct > solution):
        solution = splitproduct


print solution

When I try to run this, I get the error

TypeError: list indices must be integers, not tuple

I guess when I iterate through splitnum, x is a tuple. I need it to be an integer so I can use split5() correctly.

New code:

def split_number(number, n):

    line = str(number)

    split = [line[i:i+n] for i in range(1, len(line)-n+1, n)]

    return split


number =

while len(split_number(number,1)) is not 0:

    splitnum = split_number((number), 5)

    solution = 0

    for x in splitnum[:-1]:
        split5 = split_number(x, 1)
        for n in split5:
            splitproduct = reduce(lambda x, y: x*y, n)
        if (splitproduct > solution):
            solution = splitproduct

    number = split_number(number, 1)
    del number[0]



print solution

Now I'm getting a memory error on the 'split' line in function split_number. that's probably because of the extremely long number. But that isn't the topics question, I just wanted you guys to see how I implemented their solutions (which worked, because the program actually runs). :)

split_number([1, 2, 3, 4], 2) should yield 1, 2, 2, 3 and 3, 4, not 1, 2 and 3, 4. — Blender
– Blender, Commented Mar 9, 2013 at 0:10
To fix what Blender mentioned, change the step argument of the range inside split_number back to 1. Also you will want to set len(line)-n+1 as the maximum number so you don’t end up with four groups containing less than five numbers. — poke
– poke, Commented Mar 9, 2013 at 0:20
“Now I'm getting a memory error on the 'split' line” – The problem is that you calculate and store all the possible groups first and then want to go through it. If you combine it together and just look at a single element of the split-list (i.e. don’t calculate more), then you should be fine. — poke
– poke, Commented Mar 9, 2013 at 0:33

poke · Accepted Answer · 2013-03-09 00:18:12Z

2

Enumerate returns tuples where the first element of the tuple is the index into the sequence.

I think you just want to iterate over splitnum, and not use enumerate, since you are not using the index anywhere (for x in splitnum[:-1]).

edited Mar 9, 2013 at 0:18

poke

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answered Mar 9, 2013 at 0:08

sigpipe

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2 Comments

Tetramputechture Over a year ago

When I try that, it gives me the same error on the split5 line; that's my problem. That's why I tried using enumerate.

poke Over a year ago

@Tetramputechture When you do for x in splitnum[:-1], x will already be an element of that list. So you won’t do splitnum[x] but just x when you use it.

Blender · Accepted Answer · 2013-03-09 00:38:23Z

2

All you need to do is multiply together all 5-long substrings of your string and see which one is the biggest:

import operator

n = map(int, '7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450')

print max(reduce(operator.mul, n[i:i + 5]) for i in range(len(n) - 5))

edited Mar 9, 2013 at 0:38

answered Mar 9, 2013 at 0:13

Blender

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1 Comment

Tetramputechture Over a year ago

Ok, so instead of pasting all of that and getting the answer, I actually looked at all of those functions to see what your thought process was on this. I really learned from it, thanks!

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