Array.Take (13) .Skip (x) subtracts the take

Question

This is for Project Euler, issue 8.

I am trying to foreach through an array of numbers, each time skipping the last number and pulling out the next 13 neighboring numbers in the array.

My code is:

 for(int x = 0; x < 987; x++) { foreach(int number in numbers.Take(13).Skip(x)) { hold = hold * number; adjacent[index] = number; index++; } if (hold > product) { product = hold; } Array.Clear(adjacent, 0, adjacent.Length); index = 0; hold = 1; } 

The problem I am facing is that every time it enumerates through an array, it subtracts the amount equal to x from the number of times it goes through the list, which is 13.

So, when x is 5, it goes through the array 8 times.

How can I fix this when it moves 13 numbers at a time?

Answer 1

First, your code takes 13, and then skips the next x elements from 13 taken. Instead, skip first and then take:

  for (int x = 0; x < 987; x++) { foreach(int number in numbers.Skip(x).Take(13)) { hold = hold * number; adjacent[index] = number; index++; } if (hold > product) { product = hold; } Array.Clear(adjacent, 0, adjacent.Length); index = 0; hold = 1; } 

Answer 2

Place Skip and Take in the correct order: first Skip , then Take , for example. for a 100 digit number

  string source = string.Concat( @"73167176531330624919225119674426574742355349194934 96983520312774506326239578318016984801869478851843 85861560789112949495459501737958331952853208805511 12540698747158523863050715693290963295227443043557 66896648950445244523161731856403098711121722383113 62229893423380308135336276614282806444486645238749 30358907296290491560440772390713810515859307960866 70172427121883998797908792274921901699720888093776 65727333001053367881220235421809751254540594752243 52584907711670556013604839586446706324415722155397 53697817977846174064955149290862569321978468622482 83972241375657056057490261407972968652414535100474 82166370484403199890008895243450658541227588666881 16427171479924442928230863465674813919123162824586 17866458359124566529476545682848912883142607690042 24219022671055626321111109370544217506941658960408 07198403850962455444362981230987879927244284909188 84580156166097919133875499200524063689912560717606 05886116467109405077541002256983155200055935729725 71636269561882670428252483600823257530420752963450" .Where(c => char.IsDigit(c))); 

Linq implementation could be

  int size = 13; // or size = 4; for testing long result = Enumerable .Range(0, source.Length - size) .Select(index => source .Skip(index) .Take(size) .Select(c => (long) (c - '0')) .Aggregate((x, y) => x * y)) .Max(); // 5832 if size = 4 (test) Console.Write(result);