Thursday, April 14, 2011

Project Euler - Problem 8 - C#

/*
Find the greatest product of five consecutive digits in the 1000-digit number.
  
73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851843
85861560789112949495459501737958331952853208805511
12540698747158523863050715693290963295227443043557
66896648950445244523161731856403098711121722383113
62229893423380308135336276614282806444486645238749
30358907296290491560440772390713810515859307960866
70172427121883998797908792274921901699720888093776
65727333001053367881220235421809751254540594752243
52584907711670556013604839586446706324415722155397
53697817977846174064955149290862569321978468622482
83972241375657056057490261407972968652414535100474
82166370484403199890008895243450658541227588666881
16427171479924442928230863465674813919123162824586
17866458359124566529476545682848912883142607690042
24219022671055626321111109370544217506941658960408
07198403850962455444362981230987879927244284909188
84580156166097919133875499200524063689912560717606
05886116467109405077541002256983155200055935729725
71636269561882670428252483600823257530420752963450
 */
static int Problem8()
{
 StringBuilder data = new StringBuilder(1000);
 data.Append("73167176531330624919225119674426574742355349194934");
 data.Append("96983520312774506326239578318016984801869478851843");
 data.Append("85861560789112949495459501737958331952853208805511");
 data.Append("12540698747158523863050715693290963295227443043557");
 data.Append("66896648950445244523161731856403098711121722383113");
 data.Append("62229893423380308135336276614282806444486645238749");
 data.Append("30358907296290491560440772390713810515859307960866");
 data.Append("70172427121883998797908792274921901699720888093776");
 data.Append("65727333001053367881220235421809751254540594752243");
 data.Append("52584907711670556013604839586446706324415722155397");
 data.Append("53697817977846174064955149290862569321978468622482");
 data.Append("83972241375657056057490261407972968652414535100474");
 data.Append("82166370484403199890008895243450658541227588666881");
 data.Append("16427171479924442928230863465674813919123162824586");
 data.Append("17866458359124566529476545682848912883142607690042");
 data.Append("24219022671055626321111109370544217506941658960408");
 data.Append("07198403850962455444362981230987879927244284909188");
 data.Append("84580156166097919133875499200524063689912560717606");
 data.Append("05886116467109405077541002256983155200055935729725");
 data.Append("71636269561882670428252483600823257530420752963450");

 const int aggregation_consecutives = 5;

 // Starting point initialization
 var data_string = data.ToString();
 var global_max_mul = 0;
 var consicutives_so_far = 0;
 var local_max_mul = 1;
 var tail_num = 0;
 var current_num = 0;
  
 for (int current_char_idx = 0; current_char_idx < data.Length; current_char_idx++)
 {
  current_num = (int)data_string[current_char_idx] - '0';

  if (current_num == 0)
  {
   consicutives_so_far = 0;
   local_max_mul = 1;
   continue;
  }

  if (consicutives_so_far < aggregation_consecutives)
  {
   local_max_mul *= current_num;
   global_max_mul = Math.Max(global_max_mul, local_max_mul);

   consicutives_so_far++;

   continue;
  }

  tail_num = data_string[current_char_idx - 5] - '0';
  local_max_mul = (local_max_mul / tail_num) * current_num;
  global_max_mul = Math.Max(global_max_mul, local_max_mul);

  consicutives_so_far++;

  Console.WriteLine(string.Format(
   "current_char_idx:{0}, consicutives_so_far={1}, current_num={2} local_max_mul={3}",
   current_char_idx, consicutives_so_far, current_num, local_max_mul));
 }

 return global_max_mul;

 // Problem8: 40824
}

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