Posted By

tom76kimo on 03/01/11


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《The 3n + 1 problem》


 / Published in: C++
 

  1. #include <cstdlib>
  2. #include <iostream>
  3. #include <fstream>
  4. #include <ctime>
  5.  
  6. using namespace std;
  7.  
  8.  
  9. int three_n_plus_one(unsigned int n)
  10. {
  11. int times(1);
  12. //cout << n << " ";
  13. if(n == 1)
  14. return times;
  15.  
  16. if((n%2) == 1)
  17. times += three_n_plus_one( ((n*3)+1) );
  18. else
  19. times += three_n_plus_one( (n/2) );
  20.  
  21. return times;
  22. }
  23.  
  24. int find_max_times(unsigned int begin, unsigned int end)
  25. {
  26. int max(0);
  27. int temp_result(0);
  28. int temp_begin_end(0);
  29. if(begin > end)
  30. {
  31. temp_begin_end = end;
  32. end = begin;
  33. begin = temp_begin_end;
  34. }
  35. for(unsigned int i=begin; i<=end; ++i)
  36. {
  37. temp_result = three_n_plus_one(i);
  38. if(temp_result > max)
  39. max = temp_result;
  40. }
  41. return max;
  42. }
  43.  
  44. int main(int argv, char* argc[])
  45. {
  46. clock_t start = clock();
  47. string out_file_name(argc[1]);
  48. out_file_name.replace(5, 2, "out");
  49.  
  50. ifstream fin(argc[1], ios::in);
  51. ofstream fout(out_file_name, ios::out);
  52.  
  53. unsigned int begin(0), end(0);
  54.  
  55. while(!fin.eof())
  56. {
  57. fin >> begin;
  58. fin >> end;
  59. if(!begin || !end)
  60. {
  61. cout << "read invalid value" << endl;
  62. exit(1);
  63. }
  64.  
  65. fout << begin << " " << end << " " << find_max_times(begin, end) << " ";
  66. }
  67.  
  68. fin.close();
  69. fout.close();
  70.  
  71. cout << "cost :" << clock()-start << "ms" << endl;
  72. return 0;
  73. }

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