👀 Views: 326 💬 Answers: 1 📅 Created: 2025-06-08

algorithm pathfinding A* Java

I recently switched to I'm trying to implement the A* algorithm in Java for pathfinding in a grid-based game, but I'm running into issues with my heuristic function. I expected it to guide the search effectively towards the goal, but I'm consistently getting suboptimal paths for certain configurations of obstacles and start/goal positions. Here’s a snippet of my A* algorithm implementation: ```java import java.util.*; class Node { int x, y; double gCost, hCost, fCost; Node parent; Node(int x, int y) { this.x = x; this.y = y; } } public List<Node> aStar(Node start, Node goal) { PriorityQueue<Node> openSet = new PriorityQueue<>(Comparator.comparingDouble(n -> n.fCost)); Set<Node> closedSet = new HashSet<>(); openSet.add(start); while (!openSet.isEmpty()) { Node current = openSet.poll(); if (current.equals(goal)) { return reconstructPath(current); } closedSet.add(current); for (Node neighbor : getNeighbors(current)) { if (closedSet.contains(neighbor)) continue; double tentativeGCost = current.gCost + distance(current, neighbor); if (!openSet.contains(neighbor)) { openSet.add(neighbor); } else if (tentativeGCost >= neighbor.gCost) { continue; } neighbor.parent = current; neighbor.gCost = tentativeGCost; neighbor.hCost = heuristic(neighbor, goal); neighbor.fCost = neighbor.gCost + neighbor.hCost; } } return Collections.emptyList(); // path not found } private double heuristic(Node a, Node b) { // Using Manhattan distance as heuristic return Math.abs(a.x - b.x) + Math.abs(a.y - b.y); } ``` I’m using Manhattan distance for the heuristic, but when the grid has certain configurations of obstacles, the path chosen isn't the shortest. For example, if the start is at (0, 0) and the goal is at (4, 4) with some blocks at (2, 2) and (2, 3), my algorithm sometimes routes through (1, 1) instead of going around the obstacles effectively. I’ve verified that my neighbor generation function is correct, and I’m also checking for valid movements. I’m using Java 11 and I've tried tweaking the heuristic function to use Euclidean distance instead, but it still didn't yield better results. I'm not sure if the scenario lies in how I handle the costs or perhaps an oversight in the way I’m updating nodes in the priority queue. Any insights or suggestions on how to debug this would be greatly appreciated! Could this be a known issue? I've been using Java for about a year now. Thanks for any help you can provide!