Develop Reference

Stack overflow error in minimax algorim

Hi so I've recently started programming in java and I've set myself a task of making an AI for a tic tac toe game I've made
However the minmax algorithm is throwing a Stack Overflow error and I cant see in the error or the program where the problem is.
Here's the program:
public State minmax(boolean max, State currentState)
{
if (currentState.getNull() == 0) {
return currentState;
}
else {
State[] successorStates = currentState.getSuccessorStates(aiPlayer);
ArrayList<Integer> scoresTemp = new ArrayList<>();
for (State state : successorStates) {
scoresTemp.add(evaluate(aiPlayer, minmax(!max, state)));
}
Integer[] scores = (Integer[]) scoresTemp.toArray();
if (max) {
State maxState = successorStates[0];
int maxScore = evaluate(aiPlayer, maxState);
for (int score : scores) {
if (scores[0] > maxScore) {
maxScore = score;
maxState = successorStates[score];
}
}
return maxState;
}
else
{
State minState = successorStates[0];
int minScore = evaluate(aiPlayer, minState);
for (int score : scores) {
if (scores[0] > minScore) {
minScore = score;
}
}
return minState;
}
}
}
It returns the state which is the best move to make.
getNull() returns the amount of spaces left that can be played on.
getSuccesorStates(Player) returns all of the succeeding states of that state by making a new state of which contains the old moves and a new one of the Player.
evaluate() returns the value -1, 0 or 1 depending on a win, draw or loss in that state. None returns 0
edit:
public int getNull()
{
int amount = 0;
for (int x =0; x<9; x++)
{
if (getAllCells()[x]==null)
{
amount++;
}
}
return amount;
}
public State[] getSuccessorStates(Player player)
{
State[] states = new State[getNull()];
Player[][] stateCells = cells.clone();
int[][] nullPositions = getNulls();
for (int x=0; x<getNull(); x++)
{
stateCells[nullPositions[x][0]][nullPositions[x][1]] = player;
states[x] = new State(player, stateCells);
stateCells = cells.clone();
}
return states;
}
Caused by: java.lang.StackOverflowError
at sample.AI.minmax(AI.java:23)
at sample.AI.minmax(AI.java:32)
at sample.AI.minmax(AI.java:32)
.
.
.
23: if (currentState.getNull() == 0)
32: scoresTemp.add(evaluate(aiPlayer, minmax(!max, state)));
public Player[] getAllCells()
{
Player[] cellList = new Player[9];
for (int x = 0; x<3; x++)
{
for (int y = 0; y<3; y++)
{
cellList[y*3+x] = cells[x][y];
}
}
return cellList;
}
minmax is called in:
public Ply getPly(State state)
{
State bestState = minmax(true, state);
State[] successorStates = state.getSuccessorStates(aiPlayer);
ArrayList<State> states = new ArrayList<State>();
for (int x=0; x<successorStates.length; x++)
{
states.add(successorStates[x]);
}
int[][] nulls = state.getNulls();
Ply bestPly = new Ply(aiPlayer, nulls[states.indexOf(bestState)][0], nulls[states.indexOf(bestState)][1]);
return bestPly;
}
Thankyou if anyone could help:)

Your problem is here:
scoresTemp.add(evaluate(aiPlayer, minmax(!max, state)));
When you call the minmax method you create a bunch of data that uses up the memory ( java allows a certain amount of the computers memory to be used ).
You then inside minmax call minmax again making it create even more data and this is happening infinitely until there is no more memory left and Java throws the StackOverflow exception.

Need Help sorting out nested for loops

I'm trying to make a trivia game for my English class that will randomly pick a question, but will not pick the same one twice. I currently have a prototype set up, but I can't figure out what is going wrong that is preventing it from actually printing the questions.
Here's the behemoth:
import java.io.*;
import java.util.*;
public class qpicker
{
public static void main (String args[])
{
int qs = 0;
boolean q1checker, q2checker, q3checker, q4checker, q5checker,
q6checker, q7checker, q8checker, q9checker, q10checker, q11checker,
q12checker,q13checker, q14checker, q15checker, q16checker, q17checker,
q18checker, q19checker, q20checker; //this disaster is where i declared my
q1checker = false; //booleans
q2checker = false;
q3checker = false;
q4checker = false;
q5checker = false;
q6checker = false;
q7checker = false;
q8checker = false;
q9checker = false;
q10checker = false;
q1checker = false;
q12checker = false;
q13checker = false;
q14checker = false;
q15checker = false;
q16checker = false;
q17checker = false;
q18checker = false;
q19checker = false;
q20checker = false; //here i tried to set all booleans to false,
//thinking maybe that was the issue
do
{
qs++;
Random random = new Random();
double rng = random.nextDouble();
double selecter = rng * 10;//makes the random number easier to read
if(rng <=.5)
{
if(q1checker = false)
{
System.out.println("Put first q in here");
q1checker = true;
break;
}
}
System.out.print("cheese");//code progress tracker
if(rng <=1 && rng >.5)//this is where the question would be pulled
{
if(q2checker = false)//this ensures questions aren't repeated
{
System.out.println("Put second q in here");//display quest.
q2checker = true;
break;
}
}
System.out.print("e");
if(rng <=1.5 && rng > 1)//question picked
{
if(q3checker = false)//ensures questions aren't repeated
{
System.out.println("Put third q in here");//display quest.
q3checker = true;
break;
}
}
System.out.print("y");
if(rng <=2 && rng > 1.5 )
{
if(q4checker = false)
{
System.out.println("Put fourth q in here");
q4checker = true;
break;
}
else if (q4checker = true)
{continue;}
System.out.print(" ");
}if(rng <=2.5 && rng > 2)
{
if(q5checker = false)
{
System.out.println("Put fifth q in here");
q5checker = true;
break;
}
}
System.out.print("good");
if(rng <=3 && rng > 2.5)
{
if(q6checker = false)
{
System.out.println("Put sixth q in here");
q6checker = true;
break;
}
}
System.out.print("ness");//spells out "cheesey goodness" 20 times
}while (qs < 20);//ensures all questions are printed (in final product)
}
}

static void shuffleArray(string[] ar)
{
//set the seed for the random variable
Random rnd = ThreadLocalRandom.current();
//go from the last element to the first one.
for (int i = ar.size()- 1; i > 0; i--)
{
//get a random number till the current position and simply swap elements
int index = rnd.nextInt(i + 1);
// Simple swap
int a = ar[index];
ar[index] = ar[i];
ar[i] = a;
}
}
This way you shuffle the entire array and get the values in a random order but NO duplicate at all. Every single element changes position, so that no matter what element (position) you pick, you get a country from a random position. You can return the entire vector, the positions are random.
You could try this method, for shuffling your array and returning the entire array in random order since it mixes the elements.

From what I see you are trying to allow them to choose questions until they are exhausted, choosing randomly. You can do this easily with an ArrayList, where you pick randomly an index from the list to pull your question, remove the question from your list, so it is no longer available to choose from. Note that after you remove and use it from the list, the list will be smaller by 1
String[] questionArray = ["Question 1","Question 2","Question 3","Question 4","Question 5"];
ArrayList<String> questionList = Arrays.asList(questionArray);
//Get a random number within the range of 0..questionList.size()
int chosenIndex = 1; //Made up for simplicity
String chosen = questionList.remove(chosenIndex);
//Now that you have chosen a question, and it was removed from the list
//The list is one element smaller. Next time you get a random number
//make sure you use the range: 0..chosen.size()
System.out.println(chosen);
I believe this is what you are looking for.

You should use arrays.
Also remember that = is an assignment operator while == is comparation
This:
if(rng <=.5)
{
if(q1checker = false)
Is wrong, it should be:
if(rng <=.5)
{
if(q1checker == false)
Or better:
if(rng <=.5)
{
if(!q1checker)

Modifying ArrayList object values from another class

I have two classes: class Creature which contains ArrayList boids, and class Food.
Boids have a few parameters:
Creature(float posX, float posY, int t, int bth, int ah) {
location = new PVector(posX, posY);
vel = new PVector(random(-5,5), random(-5, 5));
acc = new PVector();
type = t;
if (t == 1) { btype = bth; }
else { health = bth; }
if (t == 1) { age = ah; }
else { hunger = ah; }
wdelta = 0.0;
action = 0;
if (btype == 1) { mass = 5.0; }
else { mass = 7.0; }
}
Food class has this method:
void foodtime(ArrayList boids) {
for (int i = 0; i < boids.size(); i++) {
Creature boid = (Creature) boids.get(i);
float distance = PVector.dist(location, boid.location);
if (distance < 0.5) {
bnumadj = i;
count++;
if (count == quantity) {
planet.food.remove(this);
count = 0;
bnumadj = -1;
}
}
}
}
What I'm trying to achieve is that if a boid "eats" the food, their boid type (btype) changes from 2 to 1.
I'm trying to use bnumadj variable to feed it back to the boid in this method:
void boid(ArrayList boids) {
for (int i = 0; i < boids.size(); i++) {
if (i == bnumadj) {
this.btype = 1;
bnumadj = -1;
}
}
}
Where am I going wrong?

This seems like a very convoluted way to do this, so I'm not surprised you're having issues. You're comparing values to indexes, which doesn't make a ton of sense to me.
Instead, try using a simple nested loop to do what you want. You can use an Iterator to make it easier to remove items while iterating.
ArrayList<Creature> boids = new ArrayList<Creature>();
ArrayList<Food> food = new ArrayList<Food>();
//populate ArrayLists
void draw(){
for(Creature boid : boids){
Iterator<Food> foodIter = food.iterator();
while(foodIter.hasNext()){
Food f = foodIter.next();
float distance = PVector.dist(boid.location, food.location);
if (distance < 0.5) {
boid.btype = 1;
foodIter.remove(); //removes the food
}
}
}
//draw the scene
}
I suppose you could move the second iteration using the Iterator inside the Creature type, but the basic idea is this: keep it simple by using an Iterator to remove the Food instead of trying to match indexes.

nearest neighbor algorithm copy element (city) to output array java

So I have a program written so far that reads in a csv file of cities and distances in the following format:
Alaska Mileage Chart,Anchorage,Anderson,Cantwell,
Anchorage,0,284,210,
Anderson,284,0,74,
Cantwell,210,74,0,
So the algorithm works and outputs the cities in the order they should be visited following the shortest path using the nearest neighbor algorithm always starting with Anchorage as the city of origin or starting city.
Using this data, the example output for the algorithm is: 1,3,2. I have ran this with a 27 element chart and had good results as well. I am using this small one for writing and debugging purposes.
Ideally the output I am looking for is the Name of the City and a cumulative milage.
Right now I am having working on trying to get the cities into an array that I can print out. Help with both parts would be appreciated or help keeping in mind that is the end goal is appreciated as well.
My thought was that ultimately I may want to create an array of {string, int}
so my output would look something like this..
Anchorage 0
Cantwell 210
Anderson 284
I am able to set the first element of the array to 1, but can not get the 2nd and 3rd element of the new output array to correct
This is the code I am having a problem with:
public class TSPNearestNeighbor {
private int numberOfNodes;
private Stack<Integer> stack;
public TSPNearestNeighbor()
{
stack = new Stack<>();
}
public void tsp(int adjacencyMatrix[][])
{
numberOfNodes = adjacencyMatrix[1].length;
// System.out.print(numberOfNodes);
// System.out.print(Arrays.deepToString(adjacencyMatrix));
int[] visited = new int[numberOfNodes];
// System.out.print(Arrays.toString(visited));
visited[1] = 1;
// System.out.print(Arrays.toString(visited));
stack.push(1);
int element, dst = 0, i;
int min = Integer.MAX_VALUE;
boolean minFlag = false;
System.out.print(1 + "\n");
//System.arraycopy(arr_cities, 0, arr_final, 0, 1); // Copies Anchorage to Pos 1 always
//System.out.print(Arrays.deepToString(arr_final)+ "\n");
while (!stack.isEmpty())
{
element = stack.peek();
i = 1;
min = Integer.MAX_VALUE;
while (i <= numberOfNodes-1)
{
if (adjacencyMatrix[element][i] > 1 && visited[i] == 0)
{
if (min > adjacencyMatrix[element][i])
{
min = adjacencyMatrix[element][i];
dst = i;
minFlag = true;
}
}
i++;
}
if (minFlag)
{
visited[dst] = 1;
stack.push(dst);
System.out.print(dst + "\n");
minFlag = false;
continue;
}
stack.pop();
}
}

Given the existing structure you are using, you can output the cities in the path using:
public void printCities(Stack<Integer> path, int[][] distances, List<String> names) {
int cumulativeDistance = 0;
int previous = -1;
for (int city: path) {
if (previous != -1)
cumulativeDistance += distances[previous][city];
System.out.println(names.get(city) + " " + cumulativeDistance);
previous = city;
}
}

I'd like to answer your question slightly indirectly. You are making life hard for yourself by using arrays of objects. They make the code difficult to read and are hard to access. Things would become easier if you create a City class with appropriate methods to help you with the output.
For example:
class City {
private final String name;
private final Map<City,Integer> connections = new HashMap<>();
public static addConnection(City from, City to, int distance) {
from.connections.put(to, distance);
to.connections.put(from, distance);
}
public int getDistanceTo(City other) {
if (connections.containsKey(other))
return connections.get(other);
else
throw new IllegalArgumentException("Non connection error");
}
}
I've left out constructor, getters, setters for clarity.
Now outputting your path becomes quite a bit simpler:
public void outputPath(List<City> cities) {
int cumulativeDistance = 0;
City previous = null;
for (City current: cities) {
if (previous != null)
cumulativeDistance += previous.getDistanceTo(current);
System.out.println(current.getName + " " + cumulativeDistance);
previous = current;
}
}

Linked List Optimization

I'm working on this program that emulates restriction enzymes and DNA splicing. I'm using DnaSequenceNode[s] as linked list nodes.
I have a problem with one of the function in my code, cutSplice() is supposed to create a new DnaStrand that is a clone of the current DnaStrand, but with every instance of enzyme replaced by splicee.
For example, if the LinkedDnaStrand is instantiated with "TTGATCC", and
cutSplice("GAT", "TTAAGG") is called, then the linked list should become something like (previous pointers not shown):
first -> "TT" -> "TTAAGG" -> "CC" -> null
My function works. However, my method cutSplice() takes more than 80 seconds to splice 200 DNAs. I'm supposed to bring that 80 seconds to 2 seconds.
This is all my code for the class : LinkedDnaStrand.java
And here's the code for the method cutSplice()
public DnaStrand cutSplice(String enzyme, String splicee) {
DnaStrand newStrand = null;
String original_Dna = this.toString();
String new_Dna = original_Dna.replaceAll(enzyme, splicee);
String[] splicee_split = new_Dna.split(splicee); // splits the new DNA string DnaStrand
newStrand = null;
int i = 0;
if (original_Dna.startsWith(enzyme)) {
newStrand = new LinkedDnaStrand(splicee);
} else {
newStrand = new LinkedDnaStrand(splicee_split[0]);
newStrand.append(splicee);
}
for (i = 1; i < splicee_split.length - 1; i++) {
String node = splicee_split[i];
newStrand.append(node);
newStrand.append(splicee);
}
newStrand.append(splicee_split[splicee_split.length - 1]);
if (original_Dna.endsWith(enzyme)) {
newStrand.append(splicee);
}
return newStrand;
}
Does anybody see anything that could make a critical difference on the time this function takes to process 200 DNAs sample?

Well, it is comfortable to use the string methods, but you are losing time in converting to the string, back to sequence, and (as pointed out in the previous comments) with the regex based string functions.
It will certainly consume less time to operate on the linked list directly, although this will require you to implement the replacement algorithm yourself:
#Override
public LinkedDnaStrand cutSplice(String enzyme, String splicee)
{
LinkedDnaStrand strand = new LinkedDnaStrand();
DnaSequenceNode end = null;
DnaSequenceNode begin = top;
int pos = 0;
DnaSequenceNode tmpStart, tmpEnd;
for (DnaSequenceNode current = top; current != null; current = current.next)
{
if(current.value != enzyme.charAt(pos))
{
tmpStart = tmpEnd = new DnaSequenceNode(begin.value);
for (DnaSequenceNode n = begin.next; n != current.next; n = n.next)
{
DnaSequenceNode c = new DnaSequenceNode(n.value);
tmpEnd.next = c;
c.previous = tmpEnd;
tmpEnd = c;
}
}
else if(++pos == enzyme.length())
{
tmpStart = tmpEnd = new DnaSequenceNode(splicee.charAt(0));
for (int i = 1; i < splicee.length(); ++i)
{
DnaSequenceNode c = new DnaSequenceNode(splicee.charAt(i));
tmpEnd.next = c;
c.previous = tmpEnd;
tmpEnd = c;
}
}
else
{
continue;
}
if(end == null)
{
strand.top = end = tmpStart;
}
else
{
end.next = tmpStart;
tmpStart.previous = end;
}
end = tmpEnd;
begin = current.next;
pos = 0;
}
return strand;
}
I do not claim that there is not any opportunity to further optimize, but this should be a lot faster as the original version. I tested it successfully with the example you gave, if you yet find a bug, feel free to fix it yourself...
Note 1: I did explicitely create a new sequence from the string (instead of using the constructor) to get the end of the sequence without having to iterate over it again.
Note 2: I assumed existing a constructor DnaSequenceNode(char value) and DnaSequenceNode having a member public char value. You might have to adjust the code appropriately if any of these assumptions fails.