Topics

C#•8mo ago

❔ Need help to optimize this simulation

For context, I'm trying to build a simulation where you start with X "nodes" and every "round", one node is replaced by one of X predetermined possibilities (.NextNodes, which may be empty) and so on until Xth round is reached. For example, we could be working with integers and on each round one of the integers we have gets +1 or +2 so if we start with 1 and 3 and play 2 rounds some of the results could be - 3 (1 + 1 + 1) and 3 - 4 (1 + 1 + 2) and 3 - 3 (1 + 2) and 4 (3 + 1) ... The aim of the simulation is to compute every possible outcome and so far it works fine with little amount of data or start nodes but if I scale up to a point where I have a few million possibilities I start feeling the slowness and if I go even further it doesn't even finish. I'm pretty sure the most important thing to do is instantiating far less lists, but I can't figure out how. I also thought about creating one task per initial node and that task would only focus on cases where its initial node is replaced in the first round to parallelize but that wouldn't fix the memory eaten by those many lists. Here's my actual method :

public static List<Node[]> ComputePossibilities(List<Node[]> currentList, int depth)
{
    if (depth == 0)
    {
        return currentList;
    }
    else
    {
        List<Node[]> ret = new();
        foreach (Node[] path in currentList)
        {
            foreach (Node node in path)
            {
                foreach (Node nextNode in node.NextNodes)
                {
                    ret.Add(path.ExceptNthOccurrenceOf(node, path.Count(x => x == node) - 1).Append(nextNode).ToArray());
                }
            }
        }

        if (ret.Count == 0)
        {
            return currentList;
        }
        else
        {
            return ComputePossibilities(ret, depth - 1);
        }
    }
}

public static List<Node[]> ComputePossibilities(List<Node[]> currentList, int depth)
{
    if (depth == 0)
    {
        return currentList;
    }
    else
    {
        List<Node[]> ret = new();
        foreach (Node[] path in currentList)
        {
            foreach (Node node in path)
            {
                foreach (Node nextNode in node.NextNodes)
                {
                    ret.Add(path.ExceptNthOccurrenceOf(node, path.Count(x => x == node) - 1).Append(nextNode).ToArray());
                }
            }
        }

        if (ret.Count == 0)
        {
            return currentList;
        }
        else
        {
            return ComputePossibilities(ret, depth - 1);
        }
    }
}

108 Replies

JakenVeina•8mo ago

so if we start with 1 and 3

how the hell does that translate into

3(1 + 1 + 1) and 3

nalka•8mo ago

well round 1 the 1 gets +1 and round 2 the 2 (that comes from 1 + 1) gets + 1, in the end we've got 3 and 3

JakenVeina•8mo ago

okay what's this for?

nalka•8mo ago

It's just in general, I've ended up doing similar algos several times and always met that issue where it works but only with little amount of data Most of the time bots on CodinGame games

JakenVeina•8mo ago

like point being

nalka•8mo ago

Gimme a sec

JakenVeina•8mo ago

is this a homework assignment of some kind?

nalka•8mo ago

Nah no homework involved School is far away now 🙂

JakenVeina•8mo ago

well, you're definitely right that instantiating fewer lists will help this is also a prime case for parallelization, as your work is all CPU-bound

nalka•8mo ago

As I said I think I should focus on eating less RAM before making it more complicated because when we reach several million possible outcomes it looks like it just stops at some point (around 1.5-2Gb)

JakenVeina•8mo ago

you can accomplish both by focusing on building a stateless solve method for solving a single case what does a "solution" look like, here? like you want to compute how MANY possible outputs there are for a particular set of input nodes? or you want to compute WHAT all the possibilities are, and list them?

nalka•8mo ago

List them

JakenVeina•8mo ago

list only the unique ones? like, there's multiple ways a simulation could play out to produce the same outputs, right? like a [1,1] could become a [2,2] by having a +1 on each one, but two different ways it could go [1,1] => [1,2] => [2,2] or [1,1] => [2,1] => [2,2] are those different outputs?

nalka•8mo ago

In the end both lists will be the same (I mean .SequenceEqual would return true) but I'd keep both in the results yes

JakenVeina•8mo ago

okay, well do you WANT those in the results? if you don't, that's a potential improvement right there

nalka•8mo ago

Yes I want those in the results

JakenVeina•8mo ago

okay

nalka•8mo ago

Obviously not keeping them would remove some lists 🙂

JakenVeina•8mo ago

there's still a potential for improvement cause you can store the results as....

var results = new Dictionary<PossibleOutcome, int>();

var results = new Dictionary<PossibleOutcome, int>();

I.E. don't store duplicates, store each possible outcome and a count of the number of times it occurred so, after computing a PossibleOutcome that you already have, you just increment the counter, and then either let the PossibleOutcome get GC'd, or put it back in a pool to get reused object/array pooling is the other big point here, I think, for reducing memory usage beyond that, I'd need to see code

nalka•8mo ago

This would be an improvement in theory but since (at least with my current method) all the results are known when you reach depth = 0 and I'd still have the plenty lists issue

JakenVeina•8mo ago

uhh.. kinda but it would be an improvement like I said the other obvious improvement to be made is to stop using lists

nalka•8mo ago

yeah that's the one I'm looking for

JakenVeina•8mo ago

all the lists are the same size, which you know ahead-of-time, use arrays instead

nalka•8mo ago

Right, that'll just make me spam arrays instead of lists but at least that's "better" spam ^^

JakenVeina•8mo ago

this, but unironically lists are heavier than arrays A) unless you're constructing your lists with the capacity parameter, the list is allocating multiple arrays over its lifetime, and the end result is a list that is extremely lilely to be over-allocated, I.E. allocated larger than what you need B) each list instance includes more allocations for state variables needed to manage the internal array

nalka•8mo ago

Yeah ik the differences or at least the most common ones Just a bad habit of using lists everywhere

JakenVeina•8mo ago

it's not a bad habit, not really develop for straightforward functionality first then optimize generally

nalka•8mo ago

Yeah but I mean I don't even think about the "optimize" part because most of the time it doesn't matter in the environments I work on

JakenVeina•8mo ago

which is normal and fine

nalka•8mo ago

So here's the array version

public static List<Node[]> ComputePossibilities(List<Node[]> currentList, int depth)
{
    if (depth == 0)
    {
        return currentList;
    }
    else
    {
        List<Node[]> ret = new();
        foreach (Node[] path in currentList)
        {
            foreach (Node node in path)
            {
                foreach (Node nextNode in node.NextNodes)
                {
                    ret.Add(path.ExceptNthOccurrenceOf(node, path.Count(x => x == node) - 1).Append(nextNode).ToArray());
                }
            }
        }

        if (ret.Count == 0)
        {
            return currentList;
        }
        else
        {
            return ComputePossibilities(ret, depth - 1);
        }
    }
}

public static List<Node[]> ComputePossibilities(List<Node[]> currentList, int depth)
{
    if (depth == 0)
    {
        return currentList;
    }
    else
    {
        List<Node[]> ret = new();
        foreach (Node[] path in currentList)
        {
            foreach (Node node in path)
            {
                foreach (Node nextNode in node.NextNodes)
                {
                    ret.Add(path.ExceptNthOccurrenceOf(node, path.Count(x => x == node) - 1).Append(nextNode).ToArray());
                }
            }
        }

        if (ret.Count == 0)
        {
            return currentList;
        }
        else
        {
            return ComputePossibilities(ret, depth - 1);
        }
    }
}

JakenVeina•8mo ago

next big optimization: get rid of that recursion

nalka•8mo ago

And go to iterative form instead?

JakenVeina•8mo ago

yup

nalka•8mo ago

Depth isn't really high in general

JakenVeina•8mo ago

true, but it still lets you control memory a little better and it's going to promote the next optimization, to parallelize this

nalka•8mo ago

Arrays made it ~25% faster (may not be accurate at all since I only put a break point on the method call and looked at elapsed time after pressing F10 instead of a proper benchmark) Iterative looks like that (and is more or less same speed)

public static List<Node[]> ComputePossibilities(List<Node[]> currentList, int depth)
{
    while (depth > 0)
    {
        List<Node[]> current = new();
        depth--;
        foreach (var path in currentList)
        {
            foreach (Node node in path)
            {
                foreach (Node nextNode in node.NextNodes)
                {
                    current.Add(path.ExceptNthOccurrenceOf(node, path.Count(x => x == node) - 1).Append(nextNode).ToArray());
                }
            }
        }

        currentList = current;
    }

    return currentList;
}

public static List<Node[]> ComputePossibilities(List<Node[]> currentList, int depth)
{
    while (depth > 0)
    {
        List<Node[]> current = new();
        depth--;
        foreach (var path in currentList)
        {
            foreach (Node node in path)
            {
                foreach (Node nextNode in node.NextNodes)
                {
                    current.Add(path.ExceptNthOccurrenceOf(node, path.Count(x => x == node) - 1).Append(nextNode).ToArray());
                }
            }
        }

        currentList = current;
    }

    return currentList;
}

JakenVeina•8mo ago

there's no way you shouldbbe allocating new lists anywhere in there also, why do you have a list as an input?

nalka•8mo ago

You talking about currentList right?

JakenVeina•8mo ago

yes

nalka•8mo ago

Hmmm most likely because the recursive had this 🤔 Removing it without just having an other local variable list doesn't seem as easy as I thought it would

JakenVeina•8mo ago

okay, I'm actually at my computer now so what is the actual goal here? like, what are the true inputs? you want to find all ways that this simulation can play out, right? what are the input parameters for this simulation? N number of "nodes" what else? the number of rounds? is that the same as the number of nodes? how about the amount added to a node during a around? your example was either +1 or +2 is that all?

nalka•8mo ago

Understanding how to fix my various simulation algorithms being bad when the number of possible outcomes gets big (millions is where I start feeling the slowness) No, they aren't related at all Well it's not directly part of the parameters but ahead of the simulation each nodes knows what it can turn into (cf .NextNodes) The simulation method is agnostic, it only knows through .NextNodes what the node may turn into but it isnt aware if (keeping the example) the current node is 1 or 73 or today's date or whatever and if the possible transofrmations are +1, ×19, turn into a random string that contains 37 characters or whatever

JakenVeina•8mo ago

I meant with regard to the simulation what are the inputs

nalka•8mo ago

Well depth and the initial nodes 🤔 Not sure if I understand your question 😅

JakenVeina•8mo ago

okay what is "depth"?

nalka•8mo ago

I mean the number of "rounds"

JakenVeina•8mo ago

k and how do we define node transformations?

nalka•8mo ago

You mean how do we compute .NextNodes?

JakenVeina•8mo ago

sure

nalka•8mo ago

It's computed before, doesn't take long enough to be worth optimizing

JakenVeina•8mo ago

so point being it's arbitrary you want to be able to run this simulation for any arbitrary type of node that you want to define

nalka•8mo ago

If you mean that it doesn't respect a pattern or whatever, yes

JakenVeina•8mo ago

you gave an example where it's integers you could, say, have each node be a chess board or pieces on a chess board

nalka•8mo ago

And the .NextNdoes for a board be the board after every possible move yeah

JakenVeina•8mo ago

k cracks knuckles also, you're only interested in the possible final state of each simulation not how you get there

nalka•8mo ago

yes and no, given I want to list all the possible outcomes (possibly dealing with the duplicate outcomes with a dictionnary as you suggested yesterday) I'm not sure I can get rid of intermediate states completely

JakenVeina•8mo ago

.... so, yes

I want to list all the possible outcomes

you don't want to list all possible paths to all possible outcomes

nalka•8mo ago

Yeah I don't care about the paths themselves, as long as I know I have X paths leading to given outcome I'm fine

JakenVeina•8mo ago

k is .NextNodes deterministic? from the current node?

nalka•8mo ago

You mean like if I have two nodes that are 1 (keeping the integer example), will both have the same .NextNodes?

JakenVeina•8mo ago

yes

nalka•8mo ago

then yes

JakenVeina•8mo ago

crap okay moment of truth nope alright, I think we're done

public static async Task Main()
{
    var simulator = new TestSimulator();

    var results = await simulator.ExecuteAsync(
        initialNodes:   new[] { 1, 1 },
        maxDepth:       2);

    foreach(var result in results)
        Console.WriteLine($"[{result.Key.Nodes[0]}, {result.Key.Nodes[1]}]: {result.Value}");
}

public static async Task Main()
{
    var simulator = new TestSimulator();

    var results = await simulator.ExecuteAsync(
        initialNodes:   new[] { 1, 1 },
        maxDepth:       2);

    foreach(var result in results)
        Console.WriteLine($"[{result.Key.Nodes[0]}, {result.Key.Nodes[1]}]: {result.Value}");
}

[2, 2]: 2
[3, 1]: 1
[4, 1]: 2
[3, 2]: 2
[2, 3]: 2
[1, 3]: 1
[1, 4]: 2
[5, 1]: 1
[3, 3]: 2
[1, 5]: 1

[2, 2]: 2
[3, 1]: 1
[4, 1]: 2
[3, 2]: 2
[2, 3]: 2
[1, 3]: 1
[1, 4]: 2
[5, 1]: 1
[3, 3]: 2
[1, 5]: 1

that seems to be correct for the "+1 or +2" simulation for depth 3

[5, 1]: 3
[6, 1]: 3
[4, 2]: 6
[3, 2]: 3
[2, 3]: 3
[2, 4]: 6
[4, 3]: 6
[4, 1]: 1
[3, 3]: 6
[5, 2]: 3
[3, 4]: 6
[1, 4]: 1
[1, 5]: 3
[2, 5]: 3
[1, 6]: 3
[3, 5]: 3
[1, 7]: 1
[7, 1]: 1
[5, 3]: 3

[5, 1]: 3
[6, 1]: 3
[4, 2]: 6
[3, 2]: 3
[2, 3]: 3
[2, 4]: 6
[4, 3]: 6
[4, 1]: 1
[3, 3]: 6
[5, 2]: 3
[3, 4]: 6
[1, 4]: 1
[1, 5]: 3
[2, 5]: 3
[1, 6]: 3
[3, 5]: 3
[1, 7]: 1
[7, 1]: 1
[5, 3]: 3

JakenVeina•8mo ago

No description

JakenVeina•8mo ago

good CPU utilization 1 billion nodes processed... loooool, GC collections are like a 5 second affair

Max Depth:          15
Simulation Time:    00:11:54.7529864
Unique Results:     361
Total Results:      1,073,741,824

Max Depth:          15
Simulation Time:    00:11:54.7529864
Unique Results:     361
Total Results:      1,073,741,824

yeah, so this particular implementation is HEAVILY memory-bound CPU utilization drops below 50% if I put a limit on how many node sets can be queued up for processing, at a time that is, this particular implementation of a simulation where calculating next nodes is just a couple of int additions so long as the average node number of forward nodes that any node has is greater than one, memory use will grow exponentially might not actually be worth all the parallelism, then I'll have to run the next test with memory throttling, both with and without parallelism

Max Depth:          15
Simulation Time:    00:07:28.2417893
Unique Results:     361
Total Results:      1,073,741,824

Max Depth:          15
Simulation Time:    00:07:28.2417893
Unique Results:     361
Total Results:      1,073,741,824

much better with release build and no debugger okay, that is noooooooooooooot finishing, with the memory throttling in place might've even deadlocked, I dunno yeah, parallelism is doing more harm than good here

Max Depth:          15
Simulation Time:    00:04:15.3034013
Unique Results:     361
Total Results:      1,073,741,824

Max Depth:          15
Simulation Time:    00:04:15.3034013
Unique Results:     361
Total Results:      1,073,741,824

nalka•8mo ago

Hmmm you reached a higher number of results than I do, I tend to be stuck (because of the memory issues) at around 50m results (should probably try in release and outside of vs to see if it helps going furether)

JakenVeina•8mo ago

the memory is definitely an issue here I max out my 32GB

nalka•8mo ago

Oh ok that explains 😄

JakenVeina•8mo ago

I think I know how to approach it better, but I also think that approach will eliminate any possibility of parallelism

nalka•8mo ago

Those damn lists 😬

JakenVeina•8mo ago

which I was rather going for in the first place no lists used all arrays with pooling oh my blazebin seems to be busted on Firefox

nalka•8mo ago

Well l guess we can start from here and see afterwards 🤷‍♂️

JakenVeina•8mo ago

https://paste.mod.gg/wojbxyvhasvo/0

BlazeBin - wojbxyvhasvo

A tool for sharing your source code with the world!

nalka•8mo ago

Ok that looks too complicated to look at on phone 😅 Brb when my pc is ready

JakenVeina•8mo ago

heh doesn't help it's all shoved into one file

nalka•8mo ago

Yeah but on pc I can copy paste on different files and make it easier to browse 😁 If I understand correctly, your version computes transformation results on the fly and always applies the same transformations (+1 or +2)?

JakenVeina•8mo ago

that was the example you proposed but yes, that's definitely the way you want to do it A) you avoid needing an allocation to store the next nodes for each node, because it gets deferred to the simulator you can generate the nodes directly into the simulator's already-allocated queue for processing B) you don't und up running the next-nodes calculation an extra billion times, for all the max-depth nodes that won't use them

nalka•8mo ago

I'm not sure if I understand this, I mean using my initial implementation you don't compute next nodes billion times (well if we use the integer example and keep it unbounded, you have to process every integer so still a lot), if say there are million or even billion possible outcomes but only X possible nodes, you'll just compute next nodes X times. While if your implementation meets (back to the integer example) a 3 two times, it'll compute the 3's next nodes twice right?

JakenVeina•8mo ago

I'm referring to your implementation of .NextNodes which, admittedly, I haven't look at, but you said it's pre-calculated if the final result of 15 rounds has 1 billion result nodes, then you are pre-calculating the .NextNodes property of each of those 1 billion nodes, even though you're not going to navigate those .NextNodes valued is that not accurate?

nalka•8mo ago

I don't think so As I said, the integers example is not really good for this because they can go as far as you like but say we're sure we'll never haves node that go above 10 and below 0 Pre-calculation will determine what the possible NextNodes are for 0, 1, 2, 3... up to but 10. Say every node's NextNodes are either the node with +1 or the node with +2 (to keep the same transformations as before) and if that'd make you go above 10, start from 0 (so 10's NextNodes are the nodes that contain 0 and 1) Here you'd only compute .NextNodes 11 times

JakenVeina•8mo ago

so, .NextNodes is pre-calculated, and also pulled from a shared cache?

nalka•8mo ago

Hmmm yeah

JakenVeina•8mo ago

mm-kay

nalka•8mo ago

Not really related but I've tried a Stack<T> based approach to try fixing memory issues by not computing every outcome simultaneously but it's not completely working atm, what do you think?

JakenVeina•8mo ago

a Stack<T> would definitely be appropriate for tracking iteration progress

nalka•8mo ago

Yeah that's kind of what I do atm, even if I think I do it pretty bad cause the Stack actually stores the index of the transformed node, the index of the next nodes and the node array representing the current state

JakenVeina•8mo ago

well, that runs significantly better, but it's also wrong... there we go

Max Depth:          15
Simulation Time:    00:01:41.1029706
Unique Results:     361
Total Results:      1,073,741,824

Max Depth:          15
Simulation Time:    00:01:41.1029706
Unique Results:     361
Total Results:      1,073,741,824

betcha I can do better

nalka•8mo ago

You used Stack<T>? Or just improved you previous alg?

JakenVeina•8mo ago

rewrote it a fair bit it's now essentially allocation-free whole program peaked at 11MB

JakenVeina•8mo ago

https://paste.mod.gg/sxuwtfmplhcm/0

BlazeBin - sxuwtfmplhcm

A tool for sharing your source code with the world!

nalka•8mo ago

Played around with your impl a little, it crashes when it meets a dead-end (node with no next nodes) On the other hand, cool thing is it can be used with pre-calculated .NextNodes (even if I guess your caching system probably becomes unneeded since the cache is already in the pre-calc) pretty easily since I just have to implement like that

public sealed class TestSimulator : Simulator<Node>
{
    protected override IReadOnlyList<Node> GetNextNodes(Node node) => node.NextNodes;
}

public sealed class TestSimulator : Simulator<Node>
{
    protected override IReadOnlyList<Node> GetNextNodes(Node node) => node.NextNodes;
}

JakenVeina•8mo ago

yeah

nalka•8mo ago

looks like adding

if (nextNodeIndex >= nextNodes.Count)
{
    goto DEPTH_RETURN;
}

if (nextNodeIndex >= nextNodes.Count)
{
    goto DEPTH_RETURN;
}

Before the line it crashes on fixes it, but given I don't have a full understanding of your code yet, not sure if it's enough/doesn't break other stuff

Accord•8mo ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

nalka•8mo ago

Looks like it's still bugged when actual depth is lower than maxDepth, at that point it returns 0 results

JakenVeina•8mo ago

so, the algorithm goes straight from retrieving the set of next nodes, into doing the replacement for the first one, and checking it for either being a solution, or being a new depth to explore you just need a bounds check there if the set of next nodes is empty, skip to the next loop iteration I.E. wrap the whole logic for the nextNodes sub-loop in a bounds check although, doing that breaks the goto maybe we can get rid of the goto actually meh, even simpler

if ((nextNodes is null)
    && !nextNodesCache.TryGetValue(currentNodes[nodeIndex], out nextNodes))
{
    nextNodes = GetNextNodes(currentNodes[nodeIndex]);
    nextNodesCache.Add(currentNodes[nodeIndex], nextNodes);
    nextNodeIndex = 0;
}

if (nextNodeIndex >= nextNodes.Count)
    goto NEXT_CURRENT_NODE;

replacedNode = currentNodes[nodeIndex];
currentNodes[nodeIndex] = nextNodes[nextNodeIndex];

if (depthStateStack.Count == (maxDepth - 1))
{
    var nodeSet = nodeSetBuilder.CreateFrom(currentNodes);

    if (results.ContainsKey(nodeSet))
    {
        results[nodeSet] += 1;
        nodeSetBuilder.Return(nodeSet);
    }
    else
        results.Add(nodeSet, 1);
}
else
{
    depthStateStack.Push(new()
    {
        NextNodeIndex   = nextNodeIndex,
        NextNodes       = nextNodes,
        NodeIndex       = nodeIndex,
        ReplacedNode    = replacedNode
    });

    nodeIndex = 0;
    nextNodes = null;
    nextNodeIndex = 0;
    continue;
}

DEPTH_RETURN:
currentNodes[nodeIndex] = replacedNode;

++nextNodeIndex;
if (nextNodeIndex < nextNodes.Count)
    continue;

NEXT_CURRENT_NODE:
nextNodes = null;
nextNodeIndex = 0;

++nodeIndex;
if (nodeIndex < currentNodes.Length)
    continue;

if (depthStateStack.TryPop(out var state))
{
    nextNodeIndex   = state.NextNodeIndex;
    nextNodes       = state.NextNodes;
    nodeIndex       = state.NodeIndex;
    replacedNode    = state.ReplacedNode;
    goto DEPTH_RETURN;
}
else
    break;

if ((nextNodes is null)
    && !nextNodesCache.TryGetValue(currentNodes[nodeIndex], out nextNodes))
{
    nextNodes = GetNextNodes(currentNodes[nodeIndex]);
    nextNodesCache.Add(currentNodes[nodeIndex], nextNodes);
    nextNodeIndex = 0;
}

if (nextNodeIndex >= nextNodes.Count)
    goto NEXT_CURRENT_NODE;

replacedNode = currentNodes[nodeIndex];
currentNodes[nodeIndex] = nextNodes[nextNodeIndex];

if (depthStateStack.Count == (maxDepth - 1))
{
    var nodeSet = nodeSetBuilder.CreateFrom(currentNodes);

    if (results.ContainsKey(nodeSet))
    {
        results[nodeSet] += 1;
        nodeSetBuilder.Return(nodeSet);
    }
    else
        results.Add(nodeSet, 1);
}
else
{
    depthStateStack.Push(new()
    {
        NextNodeIndex   = nextNodeIndex,
        NextNodes       = nextNodes,
        NodeIndex       = nodeIndex,
        ReplacedNode    = replacedNode
    });

    nodeIndex = 0;
    nextNodes = null;
    nextNodeIndex = 0;
    continue;
}

DEPTH_RETURN:
currentNodes[nodeIndex] = replacedNode;

++nextNodeIndex;
if (nextNodeIndex < nextNodes.Count)
    continue;

NEXT_CURRENT_NODE:
nextNodes = null;
nextNodeIndex = 0;

++nodeIndex;
if (nodeIndex < currentNodes.Length)
    continue;

if (depthStateStack.TryPop(out var state))
{
    nextNodeIndex   = state.NextNodeIndex;
    nextNodes       = state.NextNodes;
    nodeIndex       = state.NodeIndex;
    replacedNode    = state.ReplacedNode;
    goto DEPTH_RETURN;
}
else
    break;

more gotos!

Accord•8mo ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

nalka•8mo ago

Don't see how it fixes the actual depth lower than max depth problem given results are still built only when maxDepth is reached 🤔

JakenVeina•8mo ago

ahhhhh, another good point

Murten•8mo ago

Normally you would probably apply Alpha–beta pruning to this problem but because you don't really have a goal you can't really do that. Still a fun problem though.

JakenVeina•8mo ago

yeah, I had a problem a while back kinda like this that I solved REALLY efficiently, with parallelization and everything but the solution there only worked because the whole problem was much more, uh.... predictable like, I can know ahead of time exactly how many possible solutions there are so, what I was able to do was literally for loop over all possible solutions from 0 to N and mathematically derive which possible solution is to be tested from that index value the early-termination angle for this problem makes it much tougher I mean, I could definitely approach this problem the same way, but it would be absurd it would be "loop over all possible permutations of nodes that could be a final result, and then walk backwards to see if it's reachable from the starting point, and how many times" you'd end up doing WAY more work

Murten•8mo ago

Yeah, this "simulation" is kinda a worst case scenario lol.

nalka•8mo ago

By "WAY more work", do you mean we'd back to the point where I was before asking? aka spamming lists so much that I run out of memory?

JakenVeina•8mo ago

just more redundant work recalculating and re-traversing chunks of the graph that you've already done before

nalka•8mo ago

Yeah or maybe try storing potential results for depth X and then trying if depth X +1 exists until either depth X + 1 doesn't exist or maxDepth is reached 🤔 Though that sounds like the starting approach that was traversing a whole depth before going to the next one

Accord•8mo ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

nalka•7mo ago

Kind of workarounded it by restarting the sim with depth -1 when it returns no results

Accord•7mo ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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