singly_linked_list.h

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#ifndef SINGLY_LINKED_LIST_CLASS
#define SINGLY_LINKED_LIST_CLASS
 
/*
*  Name   : singly_linked_list
*  Author : Chris Koeritz
**
* Copyright (c) 1998-$now By Author.  This program is free software; you can
* redistribute it and/or modify it under the terms of the GNU General Public
* License as published by the Free Software Foundation; either version 2 of
* the License or (at your option) any later version.  This is online at:
*     http://www.fsf.org/copyleft/gpl.html
* Please send any updates to: fred@gruntose.com
*/
#include "node.h"
 
namespace nodes {
 
//class node;  // forward.
 
 
class singly_linked_list : public node
{
public:
  singly_linked_list() : node(1) {}
 
  //hmmm: clean up all children?
  ~singly_linked_list() {}
 
  // symbol for the rest of the list linked here.
  static const int NEXT_NODE = 0;
 
  int elements() const;
 
  singly_linked_list *next() { return (singly_linked_list *)get_link(NEXT_NODE); }
 
  void set_next(singly_linked_list *new_next) { set_link(NEXT_NODE, new_next); }
 
  static bool has_cycle(singly_linked_list *check) {
    singly_linked_list *a = check;
    singly_linked_list *b = check;
    while ((a != NULL_POINTER) && (b!= NULL_POINTER) ) {
      a = a->next();  // move position of a forward once.
      // move position of b forward twice.
      b = b->next();
      if (b != NULL_POINTER) b = b->next();
 
      if (a == b) {
        // argh, our single skipper and double skipper have arrived at the same node.
        // the only way that can happen is if there's a cycle in the list.
        return true;
      }
    }
    // if we fell out of the list iteration with a null for either pointer,
    // then there was no cycle in the list.
    return false;
  }
 
private:
  // not permitted.
  singly_linked_list(const singly_linked_list &);
  singly_linked_list &operator =(const singly_linked_list &);
};
 
} // namespace.
 
#endif