Project euler 8th question

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The four adjacent digits in the 1000-digit number that have the greatest product are 9 × 9 × 8 × 9 = 5832.

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

Find the thirteen adjacent digits in the 1000-digit number that have the greatest product. What is the value of this product?

I am getting this [96889010407]. I am printing a list but its giving just one item in list which is not desirable

What I have tried:

Python

n = 7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450
while n>0:
	count  = 0
	maximp = []
	pro = 1
	while count < 13:
		num = n%10
		pro *= num
		count += 1
	maximp += [pro]
	n = n//10
print(maximp)

Posted 17-Jul-19 2:20am

Member 14517556

Updated 17-Jul-19 4:29am

v3

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Dave Kreskowiak 17-Jul-19 9:17am

I don't know PHP, but from the looks of things, your entire approach is wrong.

You should be converting that huge string of numbers into an array of integers first, then multiply the first 5 array items together and store the result in another array. Then move over one array item and multiple the next 5 together, and so on. Sort the result array and you've got your answer.

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Richard MacCutchan · Accepted Answer · 2019-07-17T04:30:00

A much simpler method is to use a string as input and extract succeeding groups of digits. Something like the following:

Python

    n = "73167176531330624919225119674426574742" # the string of digits
    max = 0                                # the largest product
    number = ""                            # the number that makes the largest product
    ndigits = 5                            # the number of digits to use for each group
    first = 0                              # start at the first digit
    while first < len(n) - (ndigits - 1):  # process each complete set
        last = first + ndigits             # the last digit in the group
        num = n[first:last]                # extract the substring of digits
#        print("Next", num)
        total = 1;                         # start calculating
        for i in num[:]:                   # 
            total *= int(i)                # multiply the digits together
        print("Total", total)
        if total > max:                 # is this bigger than the current maximum value?
            max = total                    # yes, so replace it
            number = num                   # save the number that makes the value
        first += 1                         # set start index to the next group

    print("Biggest:", number, "Product:", max)

Patrice T · Accepted Answer · 2019-07-17T03:38:00

Quote:
I am getting this [96889010407]. I am printing a list but its giving just one item in list which is not desirable

The value is 7^13 because your code is wrong. I see no code to select the greatest product.

Python

while n>0:
	count  = 0
	maximp = [] # here you kill the list
	pro = 1
	while count < 13:
		num = n%10 # here you extract 13 times the same digit
		pro *= num
		count += 1
	maximp += [pro]
	n = n//10
print(maximp)

Your code do not behave the way you expect, or you don't understand why !

There is an almost universal solution: Run your code on debugger step by step, inspect variables.
The debugger is here to show you what your code is doing and your task is to compare with what it should do.
There is no magic in the debugger, it don't know what your cpde is supposed to do, it don't find bugs, it just help you to by showing you what is going on. When the code don't do what is expected, you are close to a bug.
To see what your code is doing: Just set a breakpoint and see your code performing, the debugger allow you to execute lines 1 by 1 and to inspect variables as it execute.

Debugger - Wikipedia, the free encyclopedia[^]

Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[^]
Basic Debugging with Visual Studio 2010 - YouTube[^]

27.3. pdb — The Python Debugger — Python 3.6.1 documentation[^]
Debugging in Python | Python Conquers The Universe[^]
pdb – Interactive Debugger - Python Module of the Week[^]

The debugger is here to only show you what your code is doing and your task is to compare with what it should do.

Project euler 8th question

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