stlastar.h

基于stl的a star寻路算法的高效实现

/*
A* Algorithm Implementation using STL is
Copyright (C)2001-2005 Justin Heyes-Jones

Permission is given by the author to freely redistribute and 
include this code in any program as long as this credit is 
given where due.
 
  COVERED CODE IS PROVIDED UNDER THIS LICENSE ON AN "AS IS" BASIS, 
  WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, 
  INCLUDING, WITHOUT LIMITATION, WARRANTIES THAT THE COVERED CODE 
  IS FREE OF DEFECTS, MERCHANTABLE, FIT FOR A PARTICULAR PURPOSE
  OR NON-INFRINGING. THE ENTIRE RISK AS TO THE QUALITY AND 
  PERFORMANCE OF THE COVERED CODE IS WITH YOU. SHOULD ANY COVERED 
  CODE PROVE DEFECTIVE IN ANY RESPECT, YOU (NOT THE INITIAL 
  DEVELOPER OR ANY OTHER CONTRIBUTOR) ASSUME THE COST OF ANY 
  NECESSARY SERVICING, REPAIR OR CORRECTION. THIS DISCLAIMER OF 
  WARRANTY CONSTITUTES AN ESSENTIAL PART OF THIS LICENSE. NO USE 
  OF ANY COVERED CODE IS AUTHORIZED HEREUNDER EXCEPT UNDER
  THIS DISCLAIMER.
 
  Use at your own risk!

*/

// used for text debugging
#include <iostream>
#include <stdio.h>
//#include <conio.h>
#include <assert.h>

// stl includes
#include <algorithm>
#include <set>
#include <vector>

using namespace std;

// fast fixed size memory allocator, used for fast node memory management
#include "fsa.h"

// Fixed size memory allocator can be disabled to compare performance
// Uses std new and delete instead if you turn it off
#define USE_FSA_MEMORY 1

// disable warning that debugging information has lines that are truncated
// occurs in stl headers
#pragma warning( disable : 4786 )

// The AStar search class. UserState is the users state space type
template <class UserState> class AStarSearch
{

public: // data

	enum
	{
		SEARCH_STATE_NOT_INITIALISED,
		SEARCH_STATE_SEARCHING,
		SEARCH_STATE_SUCCEEDED,
		SEARCH_STATE_FAILED,
		SEARCH_STATE_OUT_OF_MEMORY,
		SEARCH_STATE_INVALID
	};


	// A node represents a possible state in the search
	// The user provided state type is included inside this type

	public:

	class Node
	{
		public:

			Node *parent; // used during the search to record the parent of successor nodes
			Node *child; // used after the search for the application to view the search in reverse
			
			float g; // cost of this node + it's predecessors
			float h; // heuristic estimate of distance to goal
			float f; // sum of cumulative cost of predecessors and self and heuristic

			Node() :
				parent( 0 ),
				child( 0 ),
				g( 0.0f ),
				h( 0.0f ),
				f( 0.0f )
			{			
			}

			UserState m_UserState;
	};


	// For sorting the heap the STL needs compare function that lets us compare
	// the f value of two nodes

	class HeapCompare_f 
	{
		public:

			bool operator() ( const Node *x, const Node *y ) const
			{
				return x->f > y->f;
			}
	};


public: // methods


	// constructor just initialises private data
	AStarSearch( int MaxNodes = 1000 ) :
		m_AllocateNodeCount(0),
		m_FixedSizeAllocator( MaxNodes ),
		m_State( SEARCH_STATE_NOT_INITIALISED ),
		m_CurrentSolutionNode( NULL ),
		m_CancelRequest( false )
	{
	}

	// call at any time to cancel the search and free up all the memory
	void CancelSearch()
	{
		m_CancelRequest = true;
	}

	// Set Start and goal states
	void SetStartAndGoalStates( UserState &Start, UserState &Goal )
	{
		m_CancelRequest = false;

		m_Start = AllocateNode();
		m_Goal = AllocateNode();

		assert((m_Start != NULL && m_Goal != NULL));
		
		m_Start->m_UserState = Start;
		m_Goal->m_UserState = Goal;

		m_State = SEARCH_STATE_SEARCHING;
		
		// Initialise the AStar specific parts of the Start Node
		// The user only needs fill out the state information

		m_Start->g = 0; 
		m_Start->h = m_Start->m_UserState.GoalDistanceEstimate( m_Goal->m_UserState );
		m_Start->f = m_Start->g + m_Start->h;
		m_Start->parent = 0;

		// Push the start node on the Open list

		m_OpenList.push_back( m_Start ); // heap now unsorted

		// Sort back element into heap
		push_heap( m_OpenList.begin(), m_OpenList.end(), HeapCompare_f() );

		// Initialise counter for search steps
		m_Steps = 0;
	}

	// Advances search one step 
	unsigned int SearchStep()
	{
		// Firstly break if the user has not initialised the search
		assert( (m_State > SEARCH_STATE_NOT_INITIALISED) &&
				(m_State < SEARCH_STATE_INVALID) );

		// Next I want it to be safe to do a searchstep once the search has succeeded...
		if( (m_State == SEARCH_STATE_SUCCEEDED) ||
			(m_State == SEARCH_STATE_FAILED) 
		  )
		{
			return m_State; 
		}

		// Failure is defined as emptying the open list as there is nothing left to 
		// search...
		// New: Allow user abort
		if( m_OpenList.empty() || m_CancelRequest )
		{
			FreeAllNodes();
			m_State = SEARCH_STATE_FAILED;
			return m_State;
		}
		
		// Incremement step count
		m_Steps ++;

		// Pop the best node (the one with the lowest f) 
		Node *n = m_OpenList.front(); // get pointer to the node
		pop_heap( m_OpenList.begin(), m_OpenList.end(), HeapCompare_f() );
		m_OpenList.pop_back();

		// Check for the goal, once we pop that we're done
		if( n->m_UserState.IsGoal( m_Goal->m_UserState ) )
		{
			// The user is going to use the Goal Node he passed in 
			// so copy the parent pointer of n 
			m_Goal->parent = n->parent;

			// A special case is that the goal was passed in as the start state
			// so handle that here
			if( false == n->m_UserState.IsSameState( m_Start->m_UserState ) )
			{
				FreeNode( n );

				// set the child pointers in each node (except Goal which has no child)
				Node *nodeChild = m_Goal;
				Node *nodeParent = m_Goal->parent;

				do 
				{
					nodeParent->child = nodeChild;

					nodeChild = nodeParent;
					nodeParent = nodeParent->parent;
				
				} 
				while( nodeChild != m_Start ); // Start is always the first node by definition

			}

			// delete nodes that aren't needed for the solution
			FreeUnusedNodes();

			m_State = SEARCH_STATE_SUCCEEDED;

			return m_State;
		}
		else // not goal
		{

			// We now need to generate the successors of this node
			// The user helps us to do this, and we keep the new nodes in
			// m_Successors ...

			m_Successors.clear(); // empty vector of successor nodes to n

			// User provides this functions and uses AddSuccessor to add each successor of
			// node 'n' to m_Successors
			bool ret = n->m_UserState.GetSuccessors( this, n->parent ? &n->parent->m_UserState : NULL ); 

			if( !ret )
			{

			    typename vector< Node * >::iterator successor;

				// free the nodes that may previously have been added 
				for( successor = m_Successors.begin(); successor != m_Successors.end(); successor ++ )
				{
					FreeNode( (*successor) );
				}

				m_Successors.clear(); // empty vector of successor nodes to n

				// free up everything else we allocated
				FreeAllNodes();

				m_State = SEARCH_STATE_OUT_OF_MEMORY;
				return m_State;
			}
			
			// Now handle each successor to the current node ...
			for( typename vector< Node * >::iterator successor = m_Successors.begin(); successor != m_Successors.end(); successor ++ )
			{

				// 	The g value for this successor ...
				float newg = n->g + n->m_UserState.GetCost( (*successor)->m_UserState );

				// Now we need to find whether the node is on the open or closed lists
				// If it is but the node that is already on them is better (lower g)
				// then we can forget about this successor

				// First linear search of open list to find node

				typename vector< Node * >::iterator openlist_result;

				for( openlist_result = m_OpenList.begin(); openlist_result != m_OpenList.end(); openlist_result ++ )
				{
					if( (*openlist_result)->m_UserState.IsSameState( (*successor)->m_UserState ) )
					{
						break;					
					}
				}

				if( openlist_result != m_OpenList.end() )
				{

					// we found this state on open

					if( (*openlist_result)->g <= newg )
					{
						FreeNode( (*successor) );

						// the one on Open is cheaper than this one
						continue;
					}
				}

				typename vector< Node * >::iterator closedlist_result;

				for( closedlist_result = m_ClosedList.begin(); closedlist_result != m_ClosedList.end(); closedlist_result ++ )
				{
					if( (*closedlist_result)->m_UserState.IsSameState( (*successor)->m_UserState ) )
					{
						break;					
					}
				}

				if( closedlist_result != m_ClosedList.end() )
				{

					// we found this state on closed

					if( (*closedlist_result)->g <= newg )
					{
						// the one on Closed is cheaper than this one
						FreeNode( (*successor) );

						continue;
					}
				}

				// This node is the best node so far with this particular state
				// so lets keep it and set up its AStar specific data ...

				(*successor)->parent = n;
				(*successor)->g = newg;
				(*successor)->h = (*successor)->m_UserState.GoalDistanceEstimate( m_Goal->m_UserState );
				(*successor)->f = (*successor)->g + (*successor)->h;

				// Remove successor from closed if it was on it

				if( closedlist_result != m_ClosedList.end() )
				{
					// remove it from Closed
					FreeNode(  (*closedlist_result) ); 
					m_ClosedList.erase( closedlist_result );

					// Fix thanks to ...
					// Greg Douglas <[e-mail]>
					// who noticed that this code path was incorrect
					// Here we have found a new state which is already CLOSED
					// anus
					
				}

				// Update old version of this node
				if( openlist_result != m_OpenList.end() )
				{	   

					FreeNode( (*openlist_result) ); 
			   		m_OpenList.erase( openlist_result );

					// re-make the heap 
					// make_heap rather than sort_heap is an essential bug fix
					// thanks to Mike Ryynanen for pointing this out and then explaining
					// it in detail. sort_heap called on an invalid heap does not work
					make_heap( m_OpenList.begin(), m_OpenList.end(), HeapCompare_f() );
			
				}

				// heap now unsorted
				m_OpenList.push_back( (*successor) );

				// sort back element into heap
				push_heap( m_OpenList.begin(), m_OpenList.end(), HeapCompare_f() );

			}

			// push n onto Closed, as we have expanded it now

			m_ClosedList.push_back( n );