Best way of implementing a multi-node tree in C++? (or C#, a close cousin)

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raylopez99

What's the best way of implementing a multi-node tree in C++? What I'm
trying to do is traverse a tree of possible chess moves given an intial
position (at the root of the tree). Since every chess position has
around 30 moves, it would mean every node of the tree would have 30
branches (on average), which in turn themselves would average about 30
branches each.

I can think of a variety of ways of implementing this, including a
series of linked lists all pointing to the same header node at the
root, but I would like to know if there's a practical 'best' way, since
the tree will be traversed often, and it must be traversed quickly.
There will be no additions to the tree besides making it grow bigger
(longer, as move moves are added in a sequence). Certain branches will
be pruned, but the tree does not have to be rebalanced after pruning
(meaning the pruned branches will be simply marked as pruned but can
stay where they are).

Ideally I would like something already found in the .NET Standard
Collection Classes or Generic Collection classes, which include:
SortedList (key/value collection) and KeyedCollection, which are kinds
of Sets/Maps it appears.

BTW, nearly every reference I look shows as the sole example of tree a
red-black binary tree, which is not that helpful to me, though I
realize probably as a mathematical matter you can parse any multnode
tree into a red-black binary tree.

Thanks,

RL

Refs:

http://en.wikipedia.org/wiki/Standard_Template_Library#Containers

http://en.wikipedia.org/wiki/Set_(computer_science)
 
Well, since I've actually written a strong playing chess engine I think
I can help. My first question is...are you actually wanting to write
an intelligent engine or just scan all of the possible moves?
What's the best way of implementing a multi-node tree in C++? What I'm
trying to do is traverse a tree of possible chess moves given an intial
position (at the root of the tree). Since every chess position has
around 30 moves, it would mean every node of the tree would have 30
branches (on average), which in turn themselves would average about 30
branches each.
Click to expand...

The best way is to not store the moves at all. The branching factor,
which I think is a little higher than 30, will cause the tree to grow
so quickly that you'll run out of memory. The complexity of the tree
is O(b^n) where b is the average branching factor and n is the number
plies. Do the numbers. It's not pretty.
I can think of a variety of ways of implementing this, including a
series of linked lists all pointing to the same header node at the
root, but I would like to know if there's a practical 'best' way, since
the tree will be traversed often, and it must be traversed quickly.
There will be no additions to the tree besides making it grow bigger
(longer, as move moves are added in a sequence). Certain branches will
be pruned, but the tree does not have to be rebalanced after pruning
(meaning the pruned branches will be simply marked as pruned but can
stay where they are).
Click to expand...

It really depends on what the intent of the application is. Are you
asking because you want to create an intelligent player or just scan
the possible moves?
Ideally I would like something already found in the .NET Standard
Collection Classes or Generic Collection classes, which include:
SortedList (key/value collection) and KeyedCollection, which are kinds
of Sets/Maps it appears.
Click to expand...

None of those will work.
BTW, nearly every reference I look shows as the sole example of tree a
red-black binary tree, which is not that helpful to me, though I
realize probably as a mathematical matter you can parse any multnode
tree into a red-black binary tree.
Click to expand...

A red-black has a specific purpose. It happens to be the one of the
most common implementation for sorted dictionaries. A sorted
dictionary has absolutely nothing to do with decision trees. No, you
can't transform a decision tree into a red-black tree.
 
Thanks Brian Gideon for replying! My comments below.

Brian said:
Well, since I've actually written a strong playing chess engine I think
I can help. My first question is...are you actually wanting to write
an intelligent engine or just scan all of the possible moves?
Click to expand...

I just program for fun, as a hobby. Since I also play chess, I figured
I would write a two-ply alpha-beta algorithm for generating the best
moves from any given position (within this event horizon). I have a
number of books on this subject (some with pseudo-code), so I'm
generally familiar with the subject (as a amateur). If you have open
source code (dumbed down or otherwise, since from what I can tell the
"move ordering" algorithm is the proprietary part of any chess engine,
since, like you say, after around ply 4 you cannot exhaustively search
the entire chess tree), please feel free to send it my way or otherwise
post it in some FTP public directory)
The best way is to not store the moves at all. The branching factor,
which I think is a little higher than 30, will cause the tree to grow
so quickly that you'll run out of memory. The complexity of the tree
is O(b^n) where b is the average branching factor and n is the number
plies. Do the numbers. It's not pretty.
Click to expand...

Very interesting! So you would have a predefined way of traversing the
tree and perform "alpha-beta" (from memory, sorry if my lingo is off)
"on the fly", with a suitable cutoff, pruning the tree as you go from
right to left or whatever order you traverse. Never even thought of
this. Then you can store the best moves in a stack and pop/push the
winner candidate moves to the top of the stack. Very clever, as this
saves memory (if this is what was in mind). BTW it amazes me that
ChessBase commercial computer programs can find the best move X% of the
time (with X around 90% it seems) with just five seconds of time
elapsed. The way I code, I can't get anything to work that fast (and
it seems C++.NET is very resource hog intensive--getting a console
"Hello World" appl to run seems to take a few seconds on a modern
Pentium 4 system, LOL.
It really depends on what the intent of the application is. Are you
asking because you want to create an intelligent player or just scan
the possible moves?
Click to expand...

Actually both. Though I would like to scan all the moves for 2 ply (I
don't think it will cost too much memory)
None of those will work.
Click to expand...

Far from me to argue with you, but I do recall a binary tree can be
made from a Map/Set (this was my motivation for writing the above).

A red-black has a specific purpose. It happens to be the one of the
most common implementation for sorted dictionaries. A sorted
dictionary has absolutely nothing to do with decision trees. No, you
can't transform a decision tree into a red-black tree.
Click to expand...

OK. Probably true, and if you say so. Though if I were betting money
some clever Russian probably could do some transformation.

Thanks for replying. Just collecting information for now. I do have
Professor Hyatt's open source code ("Crafty") but it's kind of hard for
me to follow.

RL
 
First, let me say this. Writing a chess engine is *incredibly*
difficult. But, don't get discouraged. Take it one step at a time.
I just program for fun, as a hobby. Since I also play chess, I figured
I would write a two-ply alpha-beta algorithm for generating the best
moves from any given position (within this event horizon). I have a
number of books on this subject (some with pseudo-code), so I'm
generally familiar with the subject (as a amateur).
Click to expand...

Start by getting the minimax algorithm to work then move to alpha-beta
pruning.
If you have open
source code (dumbed down or otherwise, since from what I can tell the
"move ordering" algorithm is the proprietary part of any chess engine,
since, like you say, after around ply 4 you cannot exhaustively search
the entire chess tree), please feel free to send it my way or otherwise
post it in some FTP public directory)
Click to expand...

There are plenty of resources available on the net. You just have to
know what to google for. Don't worry about move ordering right now.
Take small steps. Get the minimax algorithm working, then add
alpha-beta pruning, and then worry about move ordering. Here's a
resource I've used in the past. Hopefully that will get you started.

http://www.seanet.com/~brucemo/topics/topics.htm
Very interesting! So you would have a predefined way of traversing the
tree and perform "alpha-beta" (from memory, sorry if my lingo is off)
"on the fly", with a suitable cutoff, pruning the tree as you go from
right to left or whatever order you traverse. Never even thought of
this.
Click to expand...

Yes, I suppose that's one way of looking at it. The important thing is
that you prune so that you don't have to even examine parts of the
tree. Let me back track a little bit though. It is good to store
small parts of the tree. It's usually done in what's called a
transposition table which has a fixed and limited size. It's purpose
is to recognize positions that have already been examined. Chess is a
game where different paths can lead to the same position.
Then you can store the best moves in a stack and pop/push the
winner candidate moves to the top of the stack. Very clever, as this
saves memory (if this is what was in mind).
Click to expand...

Yep, all of these algorithms visit one node at a time and use the
function call stack to do so. An actual tree is never really built in
memory.
BTW it amazes me that
ChessBase commercial computer programs can find the best move X% of the
time (with X around 90% it seems) with just five seconds of time
elapsed. The way I code, I can't get anything to work that fast (and
it seems C++.NET is very resource hog intensive--getting a console
"Hello World" appl to run seems to take a few seconds on a modern
Pentium 4 system, LOL.
Click to expand...

Those programs are *incredibly* sophisticated. Their speed comes from
a combination of the algorithms that are used and how a position is
represented. For example, the algorithms don't stop at alpha-beta.
There's the principal variation search (PVS) and MTD(f) algorithms that
are generally better. I believe most (?) engines use a form of the PVS
algorithm. The way a position is represented is also important. Most
use a bitboard strategy where the position is completely defined in
small number 64-bit fields. That way moves are generated by doing low
level bit masks and shifts.
Actually both. Though I would like to scan all the moves for 2 ply (I
don't think it will cost too much memory)


Far from me to argue with you, but I do recall a binary tree can be
made from a Map/Set (this was my motivation for writing the above).
Click to expand...

A chess game tree isn't binary though. SortedList uses an array
implementation. You may be thinking of the SortedDictionary which uses
a red-black tree implementation. However, neither are really suitable
for storing a chess position.
OK. Probably true, and if you say so. Though if I were betting money
some clever Russian probably could do some transformation.
Click to expand...

I doubt it. First, a red-black tree is used to store key-value pairs
in a sorted order. What would it mean to store chess positions in a
sorted order anyway? Also, a red-black tree is binary so unless you
only plan on storing 2 moves per position then there's an even more
fundamental conflict.

Thanks for replying. Just collecting information for now. I do have
Professor Hyatt's open source code ("Crafty") but it's kind of hard for
me to follow.
Click to expand...

It's hard for me to follow as well. Crafty is an excellent program.
Mine couldn't even come close to beating it :(. I had mine good enough
to beat GNU Chess half the time though :)
 
Thanks again Brian Gideon for the reply.

I did not realize programming chess playing was so difficult; after all
the "eight queens" problem is a standard CSci exercise to illustrate
recursion; also moving chess pieces is a standard exercise in a C# book
I have by Deitel.

Some of the stuff about move generation with bitmaps and quiescent
search makes sense. The website link I had from a previous search;
thanks.

As a programming exercise I might just build a 2 ply chess playing
engine with min-max and no alpha-beta, in view of the work involved. I
have a book by Brian Flaming with source code on a N-th branching tree,
in view of the fact that none of the .NET or generic collection
containers seem to work for chess.

If you care to answer: which is used more often in chess--recursion or
iteration? I generally don't like recursion but for traversing a tree
perhaps it's necessary.

BTW, I recall a 'neural' learning chess program was offered in beta
form--it looked like some students resume building exercise or senior
project--if chess programming according to the alpha-beta/ min-max is
difficult, imagine a non-traditional algortihm like a neural or genetic
algorithm! http://en.wikipedia.org/wiki/Genetic_algorithm

BTW, once quantum computers are perfected, the chess tree can be solved
'instantaeously'--so in theory you can beat even the best chess
program, since the entire tree will be searched at once (sci-fi for now
though).

RL
 
Just to complete this thread, another open source code project for a
chess playing engine used for pedagogical purposes is: "grey matter" /
Gray Matter : found here:
http://gray-matter.googlecode.com/svn/trunk/src/

Trouble is, they try and do "too much" (they should have a dumbed down
version just for teaching purposes; one that doesn't even check for 50
move draw rule, en passant, etc), and it's hard to follow this code,
though you can tell roughly what they are doing.

RL
 
Of course I have. But it's one thing to beat Kasparov, another to
write a tiny chess playing program. I heard somebody even programmed
an Excel spreadsheet to play chess.

RL
 
* raylopez99 said:
I did not realize programming chess playing was so difficult;
Click to expand...

Well, if you ask me, it's easy to write a chess engine. To make it
really good is the difficult part.

Here is a simple plan:

1. Do the board and the move representation
2. Do the "do move" and "undo move" operations
3. Test it
4. Write a basic (pseudo legal) move generator
5. Test it
6. Complete the move generator: castling, en passant, promotion
7. Test it
8. If you generate pseudo legal move, write something to filter out
the illegal moves
9. Implement "perft". Use it to stress test the engine
10. Implement UCI and/or XBoard, play with Arena or Winboard
11. Implement a random player, just selects a random move from
the list of legal moves
12. Now you can play games, without any searching stuff, test!
13. Write a simple evaluation function
14. Evaluate each move and use the value add a weight factor to the
random move selector. Have fun.
15. Study MiniMax, NegaMax and Alpha-Beta. Make sure you really
understand how they work!
16. Implement it, write a move selector based on it.
17. Use the protocol to configure the search: infinite, fixed depth,
fixed node count, fixed time.
18. Add the more intelligent mode where you try to efficiently use the
remaining time for the right moves and don't waste time on on
interrupted or useless searches.
19. Complete the protocol.

Then you have a working engine. Might be hard work but it's not that
difficult. And it doesn't play too good. Then you can try to make engine
cleverer (and slower) by a more sophisticated evaluation function, or
faster and deeper searching by adding a transposition table, move
ordering, PVS or mtd(f), null move pruning, extensions, reductions,
razoring or just optimizing the code.
If you care to answer: which is used more often in chess--recursion or
iteration? I generally don't like recursion but for traversing a tree
perhaps it's necessary.
Click to expand...

Why do you dislike recursion?

A tree is recursive data structure. Traversing it by recursion is just
natural.

mfg, simon .... f'up2 rgcc, nothing to do with c#
 
Hello, RL!

I'm the primary author of Gray Matter. It's largely a 1-man project
(with just some feedback from my friends). I was searching for my own
project when I came across your message, and I'm very interested.

I like your idea of a "dumbed down" version. I may fork the code and
simplify it as far as possible. Also, how is it hard to follow? I'd
like to make it more clear! I'd appreciate your feedback, and I'd
also be glad to grant you commit privileges.

Thanks,
Raj
 
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