tpl_test_cycle.H

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/*
                          Aleph_w
 
  Data structures & Algorithms
  version 2.0.0b
  https://github.com/lrleon/Aleph-w
 
  This file is part of Aleph-w library
 
  Copyright (c) 2002-2026 Leandro Rabindranath Leon
 
  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files (the "Software"), to deal
  in the Software without restriction, including without limitation the rights
  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  copies of the Software, and to permit persons to whom the Software is
  furnished to do so, subject to the following conditions:
 
  The above copyright notice and this permission notice shall be included in all
  copies or substantial portions of the Software.
 
  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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  SOFTWARE.
*/
 
 
# ifndef TPL_TEST_CYCLE_H
# define TPL_TEST_CYCLE_H
 
# include <ah-graph-concepts.H>
 
# include <tpl_graph.H>
# include <ah-errors.H>
 
namespace Aleph {
 
template <AlephGraph GT, ArcFilter<GT> SA = Dft_Show_Arc<GT>> 
class Test_For_Cycle
{
  mutable typename GT::Node * src = nullptr;
  SA sa;
 
  // Recursive DFS helper to detect if a path from curr returns to src
  bool test_cycle(typename GT::Node * curr) const
  {
    // Base case: found a path back to source -> cycle detected
    if (src == curr) 
      return true;
 
    // Already visited this node in current DFS -> no cycle via this path
    if (IS_NODE_VISITED(curr, Test_Cycle)) 
      return false;
 
    // Mark current node as visited
    NODE_BITS(curr).set_bit(Test_Cycle, true);
 
    // Explore all outgoing arcs from current node
    for (Node_Arc_Iterator<GT, SA> it(curr, sa); it.has_curr(); it.next_ne())
      {
        typename GT::Arc * arc = it.get_current_arc_ne();
        
        // Skip already-visited arcs to avoid infinite loops
        if (IS_ARC_VISITED(arc, Test_Cycle)) 
          continue;
 
        // Mark arc as visited
        ARC_BITS(arc).set_bit(Test_Cycle, true);
 
        // Recursively check if target node leads to a cycle
        if (test_cycle(it.get_tgt_node()))
          return true;
      }
 
    // All paths from curr explored without finding src -> no cycle
    return false; 
  }  
 
  // Main algorithm entry point
  bool test_cycle(const GT & g, typename GT::Node * s) const
  {
    ah_invalid_argument_if(s == nullptr)
      << "Test_For_Cycle: source node cannot be null";
 
    src = s;
 
    // Reset control bits for a fresh traversal
    g.reset_bit_nodes(Test_Cycle);
    g.reset_bit_arcs(Test_Cycle);
 
    // Explore all arcs adjacent to source node
    for (Node_Arc_Iterator<GT, SA> it(src, sa); it.has_curr(); it.next_ne())
      {
        typename GT::Arc * arc = it.get_current_arc_ne();
        
        // Skip already-visited arcs (shouldn't happen in first iteration)
        if (IS_ARC_VISITED(arc, Test_Cycle)) 
          continue;
 
        // Mark arc as visited
        ARC_BITS(arc).set_bit(Test_Cycle, true);
 
        // Check if target node leads back to source
        if (test_cycle(it.get_tgt_node()))
          return true;
      }
 
    // All paths explored without finding a cycle
    return false;
  }
 
public:
 
  Test_For_Cycle(SA arc_filter = SA()) : sa(arc_filter) { /* empty */ }
 
  bool operator () (const GT & g, typename GT::Node * src_node) const
  {
    return this->test_cycle(g, src_node);
  }
};
 
} // end namespace Aleph
 
 
# endif //  TPL_TEST_CYCLE_H