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  1. #include <iostream>
  2. #include <stddef.h>         // ptrdiff_t
  3. #include <type_traits>      // std::remove_cv
  4. #include <utility>          // std::move
  5. #include <vector>           // std::vector
  6.  
  7. typedef ptrdiff_t Size;
  8.  
  9. template< class Type >
  10. auto movable( Type& o )
  11.     -> typename std::remove_cv<Type>::type&&
  12. {
  13.     typedef typename std::remove_cv<Type>::type NcvType;
  14.     return std::move( const_cast<NcvType&>( o ) );
  15. }
  16.  
  17. namespace hare {
  18.  
  19.     // A non-copyable array.
  20.     template< class Item >
  21.     class NcArray
  22.     {
  23.     private:
  24.         NcArray( NcArray const& );                  // No such.
  25.         NcArray& operator=( NcArray const& );       // No such.
  26.  
  27.         std::vector<Item>   items_;
  28.  
  29.     public:
  30.         typedef typename std::vector<Item>::const_iterator Iterator;
  31.  
  32.         void append( Item v ) { items_.emplace_back( movable( v ) ); }
  33.  
  34.         auto begin() const -> Iterator { return items_.begin(); }
  35.         auto end() const -> Iterator { return items_.end(); }
  36.  
  37.         NcArray(): items_() {}
  38.  
  39.         NcArray( Item const& v )
  40.             : items_( v, 1 )
  41.         {}
  42.  
  43.         NcArray( NcArray&& other )
  44.             : items_( move( other.items_ ) )
  45.         {}
  46.     };
  47.  
  48.     template< class Item >
  49.     inline auto concat( NcArray<Item> a, Item const v )
  50.         -> NcArray<Item>
  51.     {
  52.         a.append( movable( v ) );
  53.         return movable( a );
  54.     }
  55.  
  56. }  // namespace hare
  57.  
  58. typedef hare::NcArray<int> Array;
  59.  
  60. auto collatz_aux( int const n, Array const a )
  61.     -> Array
  62. {
  63.     if( n == 1 )
  64.     {
  65.         return concat( movable( a ), 1 );
  66.     }
  67.     else if( n % 2 == 0 )
  68.     {
  69.         return collatz_aux( n / 2, concat( movable( a ), n ) );
  70.     }
  71.     else
  72.     {
  73.         return collatz_aux( 3 * n + 1, concat( movable( a ), n ) );
  74.     }
  75. }
  76.  
  77. auto collatz( int const n )
  78.     -> Array
  79. {
  80.     return collatz_aux( n, Array() );
  81. }
  82.  
  83. auto main()
  84.     -> int
  85. {
  86.     using namespace std;
  87.  
  88.     for( int const v : collatz( 5 ) )
  89.     {
  90.         cout << v << " ";
  91.     }
  92.     cout << endl;
  93. }
  94.  
Success #stdin #stdout 0s 3428KB
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5 16 8 4 2 1
https://ideone.com/M2v1EP
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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