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tsolron

Modified Breadth-First-Search Assistance

4 posts in this topic

First off, this if for a game I'm designing, but what I need help on seemed to be more in the 'general' category of programming.

 

I've worked for several hours on modifying a Python Breadth-First-Search (BFS) I had written. The goal is a search which starts at node (x,y) and adds all nodes within a distance to a vector. I use a priority queue and while loop to ensure I find the shortest path, and so I'm not using recursion.

 

My issue is that when I push back my class TMove onto the vector tiles (std::vector<TMove> tiles), it doesn't properly add it. Here's the relevant code. The specific line is #235.

 

void BFS2(int t, int moves, int levelWidth, int levelHeight, std::vector<TMove> &vect)
{
	vect.clear();

	std::set<int> visited;
	std::vector<TMove> tiles;
	int numInTiles = 0;
	std::priority_queue< std::pair<int,int>, std::vector<std::pair<int,int>>, pQueueCompare> pQueue;

	// TMove( index of Terrain in terrain, movement required to get here, parent index )
	tiles.push_back(TMove(t, 0, 0));
	pQueue.push(std::make_pair(numInTiles,0));
	numInTiles++;

 

Originally I was using a std::unique_ptr<TMove>, but the same issue was happening. I don't think it's actually initializing anything within tiles, but I'm not sure quite why. Similar code has worked in past projects.

 

 

 

Other relevant code, including the rest of the Breadth-First-Search is below.

[hr]

 

 

 

TMove.h

#ifndef TMove_H
#define TMove_H

#include "Terrain.h"
#include <memory>

class TMove
{
public:
	TMove(int Index, int Moves, int Parent);
	~TMove(void);
	int getMoves(void);
	int getIndex(void);
	int getParent(void);
private:
	int index;
	int moves;
	int parent;
};

#endif

 

TMove.cpp

#include "TMove.h"

TMove::TMove(int Index, int Moves, int Parent)
{
	index = index;
	moves = Moves;
	parent = Parent;
}

TMove::~TMove(void)
{
}

int TMove::getMoves(void)
{
	return moves;
}

int TMove::getIndex(void)
{
	return index;
}

int TMove::getParent(void)
{
	return parent;
}

 

Modified Breadth-First-Search

void BFS2(int t, int moves, int levelWidth, int levelHeight, std::vector<TMove> &vect)
{
	vect.clear();

	std::set<int> visited;
	std::vector<TMove> tiles;
	int numInTiles = 0;
	std::priority_queue< std::pair<int,int>, std::vector<std::pair<int,int>>, pQueueCompare> pQueue;

	// TMove( index of Terrain in terrain, movement required to get here, parent index )
	tiles.push_back(TMove(t, 0, 0));
	pQueue.push(std::make_pair(numInTiles,0));
	numInTiles++;

	int tempT = -1;
	int curMove = 0;

	// Keep looping while there are elements in the priority queue.
	while(pQueue.empty() == false)
	{
		// Get the current element.
		TMove current = tiles.at(pQueue.top().first);
		// Remove it from the priority queue.
		pQueue.pop();
		// Add it to the visited list and vect vector.
		//visited.insert(terrain.at(current->getIndex()));
		visited.insert(current.getIndex());
		vect.push_back(current);

		// Get data
		int index = current.getIndex();
		int X = terrain.at(index)->getX();
		int Y = terrain.at(index)->getY();
		int movement = current.getMoves();


		// Left
		if (X != 0)
		{
			tempT = current.getIndex() - 1;
			curMove = movement + terrainData[terrain.at(tempT)->getType()];
			if (curMove <= moves && visited.find(index - 1) == visited.end())
			{
				tiles.push_back(TMove(current.getIndex() - 1, curMove, index));
				pQueue.push(std::make_pair(numInTiles, curMove));
				numInTiles++;
			}
		}
		// Right
		if (X != levelWidth - 1)
		{
			tempT = current.getIndex() + 1;
			curMove = movement + terrainData[terrain.at(tempT)->getType()];
			if (curMove <= moves && visited.find(index + 1) == visited.end())
			{
				tiles.push_back(TMove(current.getIndex() + 1, curMove, index));
				pQueue.push(std::make_pair(numInTiles, curMove));
				numInTiles++;
			}
		}
		// Up
		if (Y != 0)
		{
			tempT = current.getIndex() - levelWidth;
			curMove = movement + terrainData[terrain.at(tempT)->getType()];
			if (curMove <= moves && visited.find(index - levelWidth) == visited.end())
			{
				tiles.push_back(TMove(current.getIndex() - levelWidth, curMove, index));
				pQueue.push(std::make_pair(numInTiles, curMove));
				numInTiles++;
			}
		}
		// Down
		if (Y != levelHeight - 1)
		{
			tempT = current.getIndex() + levelWidth;
			curMove = movement + terrainData[terrain.at(tempT)->getType()];
			if (curMove <= moves && visited.find(index - levelWidth) == visited.end())
			{
				tiles.push_back(TMove(current.getIndex() - levelWidth, curMove, index));
				pQueue.push(std::make_pair(numInTiles, curMove));
				numInTiles++;
			}
		}
	}
}
Edited by tsolron
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TMove::TMove(int Index, int Moves, int Parent)
{
	index = index;
	moves = Moves;
	parent = Parent;
}

 

is this an error in copy/pasting, or does your actual code has the 'index = index;' line? (note the missing capitalization of the rhs value, you're essentially assigning index to itself here)

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Wow. I'm surprised I didn't catch that, and I feel bad for not noticing. Typically I have it be something like "var = newVar", but for some reason I didn't here.

 

I tested it and the stated issue is fixed, but there's still another problem with getting the right indices when searching up/down. That should be easy enough to troubleshoot, though.

 

Thanks!

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You seem to be well on your way towards making good use of the standard C++ library there.
Some further C++ coding tips though:

If you use constructor initialisation lists, as you would ideally be, then the following is perfectly valid and will do what you expect:
TMove::TMove(int index, int moves, int parent)
    : index(index), moves(moves), parent(parent)
{}

Best practice is also to not include an empty non-virtual destructor. Just delete it. The compiler's auto-generated one will suffice.

Unlike C, it is customary in C++ to just use an empty parameter list i.e. () rather than (void)

You should have a look into const methods at some point. Basically putting const at the end of the method signature is a promise that the method does not directly modify any of the objects member variables. Although to beginners this feels like something entirely optional that you can just do sometimes to help you avoid silly mistakes, it's more than that because you'll eventually run into things where you will be prevented from doing stuff unless the methods your providing in certain places agree not to modify things. It's a good habbit to get into sooner or later.
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You seem to be well on your way towards making good use of the standard C++ library there.
Some further C++ coding tips though:

If you use constructor initialisation lists, as you would ideally be, then the following is perfectly valid and will do what you expect:

TMove::TMove(int index, int moves, int parent)
    : index(index), moves(moves), parent(parent)
{}

Best practice is also to not include an empty non-virtual destructor. Just delete it. The compiler's auto-generated one will suffice.

Unlike C, it is customary in C++ to just use an empty parameter list i.e. () rather than (void)

You should have a look into const methods at some point. Basically putting const at the end of the method signature is a promise that the method does not directly modify any of the objects member variables. Although to beginners this feels like something entirely optional that you can just do sometimes to help you avoid silly mistakes, it's more than that because you'll eventually run into things where you will be prevented from doing stuff unless the methods your providing in certain places agree not to modify things. It's a good habbit to get into sooner or later.

 

 

 

Thanks for the info, it'll be really useful, especially with the constructor part!

 

My reasoning for several of the things you pointed out is the "Class Wizard" added the (void) and empty destructor

 

With the const method statement, just to ensure I understand, you mean that you can still modify variables of the current object with getters/setters, but not by doing something like index++;?

 

Additionally, if you're familiar with pointers, do you have any suggestions with those? Either regular ones like Terrain *terrain; or with the newer ones like std::shared_ptr or std::unique_ptr? I understand (somewhat) how to use them, and I can see that they're useful, but I'm not entirely sure when I should be using them.

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