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."""
def problem_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 = 0
highest_product = 0
last_possible_start = len(to_process) - 5
while (offset < last_possible_start):
digits = [int(digit) for digit in to_process[offset:offset + 5]]
product = 1
for n in digits:
product *= n
if product > highest_product:
highest_product = product
offset += 1
return highest_product
if __name__ == '__main__':
print problem_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:
def problem_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 = 0
highest_product = 0
last_possible_start = len(to_process) - 5
while (offset < last_possible_start):
digits = [int(digit) for digit in to_process[offset:offset + 5]]
product = reduce(operator.mul, digits)
if product > highest_product:
highest_product = product
offset += 1
return highest_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:
def problem_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 = 5
sequences = [num_in_question[offset:offset + SEQUENCE_LENGTH] \
for offset in range(len(num_in_question) - SEQUENCE_LENGTH)]
nums = []
for sequence in sequences:
nums.append([int(num) for num in sequence])
return max([reduce(operator.mul, num_list) for num_list in nums])
Back to flipping out...
