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Project Euler: Problem 8
Just finished up with Problem 8. Brute-forcing
it was pretty straightforward, so I decided to play about
with some of the more functional aspects of Python. Enter
reduce. Here’s
the original version I used to solve the problem.
"""Solves Problem 8 from Project Euler."""defproblem_8(num_in_question):"""Finds and returns the greatest product of 5 consecutive digits \ of num_in_question."""to_process=str(num_in_question)offset=0highest_product=0last_possible_start=len(to_process)-5while(offset<last_possible_start):digits=[int(digit)fordigitinto_process[offset:offset+5]]product=1fornindigits:product*=nifproduct>highest_product:highest_product=productoffset+=1returnhighest_productif__name__=='__main__':printproblem_8("73167176531330624919225119674426574742355349194934\ 96983520312774506326239578318016984801869478851843\ 85861560789112949495459501737958331952853208805511\ 12540698747158523863050715693290963295227443043557\ 66896648950445244523161731856403098711121722383113\ 62229893423380308135336276614282806444486645238749\ 30358907296290491560440772390713810515859307960866\ 70172427121883998797908792274921901699720888093776\ 65727333001053367881220235421809751254540594752243\ 52584907711670556013604839586446706324415722155397\ 53697817977846174064955149290862569321978468622482\ 83972241375657056057490261407972968652414535100474\ 82166370484403199890008895243450658541227588666881\ 16427171479924442928230863465674813919123162824586\ 17866458359124566529476545682848912883142607690042\ 24219022671055626321111109370544217506941658960408\ 07198403850962455444362981230987879927244284909188\ 84580156166097919133875499200524063689912560717606\ 05886116467109405077541002256983155200055935729725\ 71636269561882670428252483600823257530420752963450")
And here’s the same problem_8 function using reduce:
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defproblem_8(num_in_question):"""Finds and returns the greatest product of 5 consecutive digits \ of num_in_question."""to_process=str(num_in_question)offset=0highest_product=0last_possible_start=len(to_process)-5while(offset<last_possible_start):digits=[int(digit)fordigitinto_process[offset:offset+5]]product=reduce(operator.mul,digits)ifproduct>highest_product:highest_product=productoffset+=1returnhighest_product
Pretty similar: 1 less line of code, 1 more line of imports, almost
identical performance. I guess it all comes down to taste. One note: if
you’re doing functional programming and need to use a function supported
by the operator module, that’s the recommended way of
doing it. Since it’s part of the standard library, it’s more obvious
what’s going on than a comparable lambda, plus they’re implemented in
C to give better performance. But since we’re getting all functional, we
might as well do it all the way. Here’s another version:
123456789101112131415
defproblem_8(num_in_question):"""Finds and returns the greatest product of 5 consecutive digits \ of num_in_question. This function expects num_in_question to be a string so we can slice it into 5-digit sequences. """SEQUENCE_LENGTH=5sequences=[num_in_question[offset:offset+SEQUENCE_LENGTH] \
foroffsetinrange(len(num_in_question)-SEQUENCE_LENGTH)]nums=[]forsequenceinsequences:nums.append([int(num)fornuminsequence])returnmax([reduce(operator.mul,num_list)fornum_listinnums])