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The 3n + 1 problem

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  1. /*
  2.  * 3np1.cpp
  3.  *
  4.  *  Created on: Feb 14, 2011
  5.  *      Author: dirk
  6.  */
  7.  
  8. #include <iostream>
  9. #include <algorithm>
  10.  
  11. inline unsigned cycle_len(unsigned n) {
  12.     unsigned c = 1;
  13.     while( n != 1 ) {
  14.         if( n % 2 ) n = 3 * n + 1;
  15.         else n = n / 2;
  16.         ++c;
  17.     }
  18.     return c;
  19. }
  20.  
  21. int main(int argc, char **argv) {
  22.     unsigned i(0), j(0), max(0), start(0), end(0);
  23.  
  24.     while (std::cin >> i) {
  25.         std::cin >> j;
  26.  
  27.         max = 0;
  28.         if(i < j) {
  29.             start = i;
  30.             end = j;
  31.         }
  32.         else {
  33.             start = j;
  34.             end = i;
  35.         }
  36.         for(unsigned x = start; x <= end; ++x) {
  37.             max = std::max(max, cycle_len(x));
  38.         }
  39.         std::cout << i << ' ' << j << ' ' << max << '\n';
  40.     }
  41. }

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