A star algorithm

Hi Everyone,
How to implement A star algorithm into the 15 x 15 maze? Herewith attached with "queue stacked search" which workable on 15 x 15 maze. Now, I want to change to another search algorithm which is called A star algorithm. Any clear instruction regarding on this method?
Many thnaks.
Attachments:
Version 1 - Copy.zip ‏59 KB

Hi Christinalau,
now that is the third thread on solving a maze, all you change is the kind of solving algorithm. Again: please stick to your original thread!
Here and here!
For all interested persons: we're discussing Christinas school homework here...
Best regards,
GerdW
CLAD, using 2009SP1 + LV2011SP1 + LV2014SP1 on WinXP+Win7+cRIO
Kudos are welcome

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Hi folks,
I just need someone to give me a little hint about
the A* (a star) algorithm to be applied on n-nary
tree. I guess some of u reading this may have good
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Hi all.
I found some open source code which implements the A Star algorithm to achieve path finding for the purpose of navigating something in a game (although it could really be used for anything). Problem is, I can't get it to work. I've e-mailed the author but no reply yet so I was hoping someone could shed some light on my situation.
The code is meant to find a path on a 2 dimensional grid filled with obstacles using the following methods:
PathFinder star = new PathFinder(grid);
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I don't understand this error at all. The findShortest method takes 4 integers and I'm passing it 4 integers! Any ideas what this error means?
Here's my Test class:
import java.util.*;
import javax.swing.plaf.basic.*;
import java.awt.event.*;
import javax.swing.*;
import java.io.*;
import javax.swing.filechooser.*;
import java.util.Random;
public class Test
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                public int giveMove() {
                    if (size() < 2)
                        return -1;
                    Position last = (Position)positions.get(size() - 1);
                    Position forlast = (Position)positions.get(size() - 2);
                    if (forlast.col - last.col == 1)
                        return 2; //down
                    else if (forlast.col - last.col == -1)
                        return 0; //up
                    else if (forlast.row - last.row == 1)
                        return 1;//right
                    else if (forlast.row - last.row == -1)
                        return 3; //left
                    return -1;
                /** list of positions */
                public List positions;
                public int getCost() { return positions.size() - 1; }
                public int size() { return positions.size(); }
                public void add(Object o) { positions.add(o); }
                /** add (r,c) to the path */
                public void add(int r, int c) {
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                public Position head() { return (Position) positions.get(0); }
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                public Path(int cap) { positions = new ArrayList(cap); }
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        /** position on the grid */
       public static final class Position
                public int row, col;
                public Position(int row, int col) {
                    this.row = row; this.col = col;
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                        for (int j=0; j < grid[counter].length; j++)
                                grid[counter][j] = 0;
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} Here's the PathFinder class I downloaded:
import java.util.*;
import javax.swing.plaf.basic.*;
import java.awt.event.*;
import javax.swing.*;
import java.io.*;
import javax.swing.filechooser.*;
import java.util.Random;
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    private final int [][] grid;
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    private final int [][] distances;
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    private boolean isEmpty(int r, int c) {
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    public PathFinder(int[][] grid) {
        this.grid = grid;
        this.distances = new int [grid.length][grid.length];
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    private void clear() {
        for (int i = 0 ; i < distances.length ; i++)
            for (int j = 0 ; j < distances.length ; j++)
distances[i][j] = Integer.MAX_VALUE;
/** position on the grid */
public final static class Position {
public int row, col;
public Position(int row, int col) {
this.row = row; this.col = col;
/** path from start to a certain position */
public final static class Path {
/** 2 for down, 0 is up, 1 is right and 3 is left */
public int giveMove() {
if (size() < 2)
return -1;
Position last = (Position)positions.get(size() - 1);
Position forlast = (Position)positions.get(size() - 2);
if (forlast.col - last.col == 1)
return 2; //down
else if (forlast.col - last.col == -1)
return 0; //up
else if (forlast.row - last.row == 1)
return 1;//right
else if (forlast.row - last.row == -1)
return 3; //left
return -1;
/** list of positions */
public List positions;
public int getCost() { return positions.size() - 1; }
public int size() { return positions.size(); }
public void add(Object o) { positions.add(o); }
/** add (r,c) to the path */
public void add(int r, int c) {
positions.add(new Position(r,c));
/** get first position */
public Position head() { return (Position) positions.get(0); }
public Path(ArrayList positions) { this.positions = positions; }
public Path(Position initial) {
positions = new ArrayList(1);
positions.add(initial);
public Path(int cap) { positions = new ArrayList(cap); }
public void set(Position front, Path old) {
positions.add(front);
Iterator i = old.positions.iterator();
while (i.hasNext())
positions.add(i.next());
/** gives the move to take for the shortest path from startRow to startCol
* 0 up, 1 right, 2 down, 3 left
* -1 if no move possible
public final int findShortest
(int startRow, int startCol, int goalRow, int goalCol) {
clear();
Position initial = new Position(startRow, startCol);
//LinkedList list = new LinkedList();
Position goal = new Position(goalRow, goalCol);
BinaireHoop list = new BinaireHoop(200, new Path(goal), goal);
list.add(new Path(initial));
Position [] successors = new Position[4];
int trie = 0;
for ( ; ! list.isEmpty() && trie < 10000 ; trie++) {
Path first = (Path) list.remove();
Position firstPos = first.head();
int r = firstPos.row; int c = firstPos.col;
if (r == goalRow && c == goalCol) { //goal found !
return first.giveMove();
} else {
int successorsCount = 0;
if (isEmpty(r-1,c)) {
successors[successorsCount++]
= new Position(r-1, c);
if (isEmpty(r+1,c)) {
successors[successorsCount++]
= new Position(r+1, c);
if (isEmpty(r,c-1)) {
successors[successorsCount++]
= new Position(r, c-1);
if (isEmpty(r,c+1)) {
successors[successorsCount++]
= new Position(r, c+1);
while (successorsCount-- > 0) {
Position succ = successors[successorsCount];
int newPathCost = first.getCost() + 1;
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if (distances[succ.row][succ.col] > newPathCost) { //shorter
distances[succ.row][succ.col] = newPathCost;
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newPath.set(succ, first);
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list.add(newPath);
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return -1;
There's also a BinaireHoop class which the PathFinder class uses. I'll post that code if anyone thinks it's relevant but the error appears to be soley on my implementation. The Path and Position and just small subclass which for the sake of quickness I just placed into my Test class too instead of into a new class to themselves.
Any thoughts appreciated! I would really like to get this working =)
Thanks.

Thanks for your reply. Doh, totally missed that one =)
Anyway, I got the code working but it's still very buggy. I think this must just be a problem with the PathFinder class I downloaded.
I create a 2D array
      int[][] array = {
                              {-1, -1, -1, -1, -1, -1, -1, -1},
                              {-1, -1, -1, -1, -1, -1, -1, -1},
                              {-1, -1, -1, -1, -1, -1, -1, -1},
                              {-1, -1, -1, -1, -1, -1, -1, -1},
                              {-1, -1, -1, -1, -1, -1, -1, -1},
                              {-1, -1, -1, -1, -1, -1, -1, -1},
                              {-1, -1, -1, -1, -1, -1, -1, -1},
                              {-1, -1, -1, -1, -1, -1, -1, -1}
                      };and choose starting and goal coordinates
int p = star.findShortest(1, 1, 2, 2);The PathFinder will generate the coordinates to move to (I just stuck it all in a loop and updated the starting coordinates as appropriate to lead me to the goal). This is great!
However, there seem to be a lot of bugs when I introduce "occupied squares". Basically, -1 in the array means that that square is empty whereas anything else means its full and the path finder should, in theory, generate a path around these obstacles. This isn't working correctly though.
Sometimes a path wil be found around the obstacle, sometimes the path will go straight through it, and many times it just throws an array index out of bounds exception error!
Anyone got any ideas? Or does anyone have any examples of a working path finder? =)
Cheers

Solution: A-Star Path Finding Algorithm (games)

Hello everyone. I have developed several A-Star implementations for games, if you come across anyone with questions relating to path finding, please direct them to [email protected]

I'll also be directing several rich Nigerians who need your help, too, if that is OK.

How to use the path generated by A star to guide the robot to move?

I now know how to use A star path planning on Voronoi and I can run this program successfully.\
however, my problem now is how i can use the path data (generated by the A* path planning algorithm) to guide the robot to drive along this path? well, i suppose i can get a series of dots (denoted by x and y coordinates) from the path, and use these dots to guide the robot ?
can anyone please help?
thank you very much
Solved!
Go to Solution.

Ravens Fan wrote:
You can't.
My post above will point everyone to the other post so that we don't have people trying to assist you in two different places without knowledge of the other thread.
thank you

Tile-based map and A-star help?

I am working on a tower defense type game. A while ago I posted asking about maze logic and was kindly directed towards A-star pathfinding. It is perfect. I understand the concept and it makes sense. Now the problem I am having is how to do the tile-based map? I'm having a hard time wrapping my head around it. I just want to do a straight square map comprised of squares. I realize a 2D Array would probably be the best way just such as:
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The reason to distribute your maze into nodes (tiles) is that pathfinding is slow, so you want to eliminate any notion of screen dimensions (pixels, inches, etc.) from A*. For all purposes, your maze is 100x100 pixels; any given object can choose between 100 horizontal and 100 vertical values.
how would I keep the enemy units moving smoothly between tiles and not just jumping to the center of each tile?Although your units may only have 100x100 nodes to consider, you can still animate them walking between each adjacent node on the path. Remember that the pathfinding (per tier) will occur before anything actually moves.
Still, this could look funny with only 100 nodes per axis. Units should use the shortest path thats visible to them, and turning several degrees at each node will look choppy. So. I list three potential solutions here:
• Increase the number of nodes (the accuracy). Speed may be an issue.
• Use path smoothing algorithm. I havent seen your circumstance, but I would generally recommend this.
• Use multi-tiered/hierarchical pathfinding. This is probably more complex to implement.
Note that although the second and third options are distinct, they may coincide (some smoothing algorithms use multiple tiers). Googling for pathfinding smoothing returned many results; this one in particular looked useful: [Toward More Realistic Pathfinding|http://www.gamasutra.com/features/20010314/pinter_01.htm]
How do I create a tile based view so that the user can only place towers on a tile(the mouse click location could be any point inside the tile)?If objects can be placed at arbitrary points, then A* needs to deem nodes impassable (your arrays 1) based on the objects placed in them. You have to be careful here and decide whether entire nodes should be ignored based on towers partial presence; for instance:
|====|====|====|====|====|
|====|====|====|===+|+++=|
|====|====|====|===+|+++=|
|====|====|====|====|====|
|0~0=|====|====|====|====|pixels: = ; node dividers: | (and line breaks for vertical) ; tower: +
The tower only covers ¼ of the node at (3, 3); should you eliminate it? Five solutions are obvious:
Ignore any node with any chunk of a tower in it.
Ignore any node entirely covered by a tower.
Ignore any node whose center is covered by a tower. This wont work with multi-tiered pathfinding.
Ignore any node that has a tower covering any point the units are required to pass through. This will work with multi-tiered pathfinding.
Using multi-tiered pathfinding, consider only consider the sub-nodes that arent covered by a tower.
I realize a 2D Array would probably be the best way just such as
int[][] map = new int[100][100]
For starters, if only want two valuespassable and impassiblethen a boolean would be better. But I would recommend against this. Id bet you could write some OO code specific to your situation. You might want to use terrain costs, where nodes exist that A* would prefer over others.
I hope I answered some of your questions. Let me know if you have moreor if I didnt.
Good luck.
Douglas

Will star transformation be scalable?

This is rather an algorithmic question
I happen to read a post about a real-world problem.
http://groups.google.com/group/comp.databases.oracle.server/browse_thread/thread/0db61c4fab79769a?hl=en
Simple back envelope analysis shows that star transformation would be very expensive in terms of storage:
The fact table F has 750 million rows, a dimensional table D has 70k rows. Suppose I have a bitmap join index between F and D to support star transformation.
How large would the bitmap index be?
70k values, each need a bitmap vector of 750M bits. The bitmap size would be 70k x (750M/8) bytes=6.6kGb. Is that too large?
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I guess my general questions is that if the dimension table's cardinality is in the order of thousands, what solution would Oracle provide? Thanks.
T.K.

Thanks for the link. However, I do not see any metrics mentioning about bitmap compression degree.
I agree that 6.6kG join bitmap index is not in the compression form. However, in general to what degree can a bitmap be compressed? In this particular example, suppose it can be compressed by a ratio of 100. Then, we still need 6.6kG/100=66G for the bitmap join index. Decompressing it on the fly also take a lot of CPUs cycles. Adding more CPU cores would not benefit since most cores share the same L2 cache. (cache misses would be a bottleneck)
Are there any benchmark results or documents discussing bitmap compression effect and showing the practical side of a reasonable large db benefiting from Star transformation like this example?
thanks,
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Hi,
I would like to know following things
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what is the solution for this type of exception.
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SHA2 Algorithm support in Adobe Acrobat 9

Hello,
1) Does Acrobat 9 supports SHA2 Hash algorithms while signing PDF file?
2) As per my understanding PDF is signed using below approach
    Step 1. Take the PDF contents
    Step 2. Calculate the Hash of the content
    Step 3. Then sign(Encrypt) the hash. (here again we calculate the hash)
So we are hashing the content twice.
If I use SHA1 algorithm in Step2 and SHA2 algorithm in Step3, Adobe 9 is able to verify the signature. But if i use SHA2 algorithm in Step1 & Step 2
Adobe 9 is saying "Content altered....."
Why so?
Please help.
Thanks in advance
Priyanka

SHA2 was only added in Acrobat 9.1. Also, the Microsoft Base CSP is needed for SHA2 support - Base CSP is included in Vista and Windows 7, but in XP it needs to be downloaded as a seperate addon.
How are you setting the values in your SecurityHandler? Off the top of my head, I believe in order to use SHA2 to hash the content (your "Step 2") you need to use AES-256 as your encryption algorithm which required a different cryptVersion be set in your SecurityHandler structure.

Why when using Adobe Bridge, I apply a star rating, the rating does not show up in Photoshop Elements? [tags]

Why when using Adobe Bridge, I apply a star rating, the rating does not show up in Photoshop Elements. I use Elements as my organizer and Bridge to view as it is much more user friendly. Anyone any solutions??

Most likely you have set the wrong file as the external editor. You don't want the obvious one; that's just a link to the welcome screen. Go back and choose this one, which is hidden away inside the folder Support Files:

A star algorithm

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