Project Euler #8 in Python:-CodePudding

I want to find the greatest product of thirteen adjacent digits in this 1000-digit number, This code works for " the four adjacent digits" but it doesn't work with "the thirteen adjacent digits", I've tried to figure out why but I couldn't.

numbers = '''73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851843
85861560789112949495459501737958331952853208805511
12540698747158523863050715693290963295227443043557
66896648950445244523161731856403098711121722383113
62229893423380308135336276614282806444486645238749
30358907296290491560440772390713810515859307960866
70172427121883998797908792274921901699720888093776
65727333001053367881220235421809751254540594752243
52584907711670556013604839586446706324415722155397
53697817977846174064955149290862569321978468622482
83972241375657056057490261407972968652414535100474
82166370484403199890008895243450658541227588666881
16427171479924442928230863465674813919123162824586
17866458359124566529476545682848912883142607690042
24219022671055626321111109370544217506941658960408
07198403850962455444362981230987879927244284909188
84580156166097919133875499200524063689912560717606
05886116467109405077541002256983155200055935729725
71636269561882670428252483600823257530420752963450'''

li = list()
for line in numbers.splitlines():
    line = line.strip()
    for number in line:
        li.append(int(number))


def multiplyList(li):
    result = 1
    for x in li:
        result *= x
    return result


multiplication_list = list()
biggest = 0
for number in li:

    if len(multiplication_list) < 13:
        multiplication_list.append(number)
    elif len(multiplication_list) == 13:
        result = multiplyList(multiplication_list)
        if result > biggest:
            biggest = result
        multiplication_list.clear()

print(biggest)

CodePudding user response：

The requirement is that you continue to look at all of the values in the list, scanning through it like a window over a moving scroll, but every time you get to 13 characters, you are starting over from the start.

Instead of clear try pop(0)

It should be noted that your approach is far from optimal. You should think about whether it is even required to re-run the multiplication every time.

CodePudding user response：

There were 2 problems with your code:

You start over when you hit 13 numbers as pointed out by @cwallenpoole
You skip a number when you hit 13 numbers

I've also replaced the 13 with a constant, and saved the characters as a string such that it's easier to figure out if something goes wrong.

Does that fix your issues?

Note: the second solution scales much better

CONSTANTS:

import timeit
DIGITS = 69
COUNT = 1_000
NUMBERS = '''73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851843
85861560789112949495459501737958331952853208805511
12540698747158523863050715693290963295227443043557
66896648950445244523161731856403098711121722383113
62229893423380308135336276614282806444486645238749
30358907296290491560440772390713810515859307960866
70172427121883998797908792274921901699720888093776
65727333001053367881220235421809751254540594752243
52584907711670556013604839586446706324415722155397
53697817977846174064955149290862569321978468622482
83972241375657056057490261407972968652414535100474
82166370484403199890008895243450658541227588666881
16427171479924442928230863465674813919123162824586
17866458359124566529476545682848912883142607690042
24219022671055626321111109370544217506941658960408
07198403850962455444362981230987879927244284909188
84580156166097919133875499200524063689912560717606
05886116467109405077541002256983155200055935729725
71636269561882670428252483600823257530420752963450'''
ALL_NUMBERS = [int(x) for x in NUMBERS.replace('\n', '')]

Recomputing approach:

def test_1():
    max_product = 0
    used_digits = []
    for i in range(len(ALL_NUMBERS) - DIGITS   1):
        multiplication_list = ALL_NUMBERS[i:i   DIGITS]
        product = 1
        for factor in multiplication_list:
            product *= factor
        if max_product < product:
            max_product = product
            used_digits = multiplication_list
    return max_product, "".join([str(i) for i in used_digits])

Alternative solution:

def test_2():
    start = max_product = 0
    current_product = 1
    skip_values = DIGITS - 1
    for i, new_number in enumerate(ALL_NUMBERS):
        if new_number == 0:
            current_product = 1
            skip_values = DIGITS - 1
        elif 0 < skip_values:
            current_product *= new_number
            skip_values -= 1
        else:
            current_product *= new_number
            if max_product < current_product:
                max_product = current_product
                start = i - DIGITS   1
            current_product //= ALL_NUMBERS[i - DIGITS   1]
    return max_product, "".join([str(i) for i in ALL_NUMBERS[start:start   DIGITS]])

Benchmark:

print("product digits")
print(*test_1())
print(*test_2())
print("#1", timeit.timeit('''test_1()''', globals=globals(), number= COUNT))
print("#2", timeit.timeit('''test_2()''', globals=globals(), number= COUNT))

Output:

product digits
2412446685431734624320887406251212800000000 863465674813919123162824586178664583591245665294765456828489128831426
2412446685431734624320887406251212800000000 863465674813919123162824586178664583591245665294765456828489128831426
#1 2.416368225000042
#2 0.1289158959989436