Ive been working on pathfinding algorithms for a couple weeks now and A Star has me stumped. Right now i am attempting to Pathfind over a maze in a matrix of the form

boolean map[x][y][5]; where index 0-3 are the walls on the cells starting on the right with 0, up being held in 1 and so on, where true means there is a wall. Index 4 is to mark the cell as visited or unvisited and is not used by my implementation of A.

For some reason I cant comprehend the search gets stuck within 10 spaces of the start and just cycles through those cells. The problem is inside the while(!openSet.isEmpty()) loop and appears to be connected to elements of the closed set being added to the open set. I based this implementation directly on the below psuedocode and it is almost a line by line match.

Here is my code:

```
public Stack AStar(int[] start, int[] end){
ArrayList<int[]> closedSet = new ArrayList<int[]>(); //stores the set of already visited cells.
ArrayList<int[]> openSet = new ArrayList<int[]>(); //stores the set of yet to be evaluated nodes which are next to evaluated nodes.
HashMap<int[], Integer> gScore = new HashMap<int[], Integer>(); //stores the cost to get to the cell stored in the form int[0] = x and int[1] = y.
HashMap<int[], Integer> hScore = new HashMap<int[], Integer>(); //stores the minimum cost to get from current cell to final cell
HashMap<int[], Integer> fScore = new HashMap<int[], Integer>(); //stores fscore = gscore + hscore
HashMap<int[], int[]> path = new HashMap<int[], int[]>(); //stores the traveled routes where first int[] is current cell and second is cell we came from
gScore.put(start, 0);
hScore.put(start, HCost(start, end));
fScore.put(start, HCost(start, end));
openSet.add(start);
while(!openSet.isEmpty()){
int[] current = openSet.get(0);
if(current.equals(end)){
Stack sPath = new Stack();
sPath.push(current);
while(current != start){
current = path.get(current);
sPath.push(current);
}
return sPath;
}
openSet.remove(current);
closedSet.add(current);
int[][] neighbors = getNeighbors(current);
for(int i = 0; i < neighbors.length; i++){
int tgScore = (int)gScore.get(current) + 1;
int[] n = {neighbors[i][0], neighbors[i][1]};
if(closedSet.contains(n)){
if(tgScore >= (int)gScore.get(n))
continue;
}
if((!openSet.contains(n) && !closedSet.contains(n)) || tgScore < (int)gScore.get(n) && closedSet.contains(n)){
path.put(n, current);
gScore.put(n, tgScore);
fScore.put(n, tgScore + HCost(n, end));
if(!openSet.contains(n)){
AddToOpen(n, fScore, openSet);
}
}
}
}
return null; //failed to find a path.
}
private int[][] getNeighbors(int[] cell){
int[][] open;
boolean a = false,b = false,c = false,d = false;
byte size = 0;
if((cell[0] + 1) <= x && !map[cell[0] + 1][cell[1]][0]) {
size++;
a = true;
}
if((cell[1] + 1) <= y && !map[cell[0]][cell[1] + 1][1]) {
size++;
b = true;
}
if((cell[0] - 1) >= 0 && !map[cell[0] - 1][cell[1]][2]){
size++;
c = true;
}
if((cell[1] - 1) >= 0 && !map[cell[0]][cell[1] - 1][3]) {
size++;
d = true;
}
open = new int[size][2];
if(d){
size--;
open[size][0] = cell[0];
open[size][1] = cell[1] - 1;
}
if(c){
size--;
open[size][0] = cell[0] - 1;
open[size][1] = cell[1];
}
if(b){
size--;
open[size][0] = cell[0];
open[size][1] = cell[1] + 1;
}
if(a){
size--;
open[size][0] = cell[0] + 1;
open[size][1] = cell[1];
}
return open;
}
private void AddToOpen(int[] n, HashMap<int[], Integer> fScore, ArrayList openSet) {
boolean found = false;
int index = 0;
if(openSet.size() <= 0){
openSet.add(n);
return;
}
if(fScore.get(openSet.get(openSet.size() - 1)).compareTo(fScore.get(n)) <= 0){
openSet.add(openSet.size() - 1, n);
return;
}
while(true){
int[] d = (int[])openSet.get(index);
if(fScore.get(d).compareTo(fScore.get(n)) > 0){
openSet.add(n);
return;
}
}
public int HCost(int[] start, int[] end){
int cost = (int) Math.sqrt((end[0] - start[0])^2 + (end[1] - start[1])^2);
return cost;
}
```

Here is the psuedocode:

```
function A*(start,goal)
closedset := the empty set // The set of nodes already evaluated.
openset := {start} // The set of tentative nodes to be evaluated, initially containing the start node
came_from := the empty map // The map of navigated nodes.
g_score[start] := 0 // Cost from start along best known path.
// Estimated total cost from start to goal through y.
f_score[start] := g_score[start] + heuristic_cost_estimate(start, goal)
while openset is not empty
current := the node in openset having the lowest f_score[] value
if current = goal
return reconstruct_path(came_from, goal)
remove current from openset
add current to closedset
for each neighbor in neighbor_nodes(current)
tentative_g_score := g_score[current] + dist_between(current,neighbor)
if neighbor in closedset
if tentative_g_score >= g_score[neighbor]
continue
if neighbor not in openset or tentative_g_score < g_score[neighbor]
came_from[neighbor] := current
g_score[neighbor] := tentative_g_score
f_score[neighbor] := g_score[neighbor] + heuristic_cost_estimate(neighbor, goal)
if neighbor not in openset
add neighbor to openset
return failure
function reconstruct_path(came_from, current_node)
if current_node in came_from
p := reconstruct_path(came_from, came_from[current_node])
return (p + current_node)
else
return current_node
```

Any and all help is greatly apreciated.

Thanks.

*Edited 3 Years Ago by DarkLightning7*