Confusion with A* Algorithm Heuristic in Java - Inconsistent Pathfinding Results
I'm wondering if anyone has experience with I tried several approaches but none seem to work. Hey everyone, I'm running into an issue that's driving me crazy. I'm implementing the A* algorithm in Java for a grid-based pathfinding system, but I'm working with inconsistent results when using different heuristics. I'm utilizing the Manhattan distance as my heuristic, but sometimes the algorithm does not yield the expected shortest path. For instance, when trying to navigate from (0, 0) to (4, 4) on a 5x5 grid with obstacles, it occasionally finds a longer path instead of the optimal one, especially when obstacles are placed strategically in the path. Here's a simplified version of my A* implementation: ```java import java.util.*; class Node { int x, y, cost, heuristic; Node parent; Node(int x, int y, int cost, int heuristic) { this.x = x; this.y = y; this.cost = cost; this.heuristic = heuristic; } int getF() { return cost + heuristic; } } public class AStar { private int[][] grid; private boolean[][] visited; public AStar(int[][] grid) { this.grid = grid; this.visited = new boolean[grid.length][grid[0].length]; } public List<Node> findPath(Node start, Node goal) { PriorityQueue<Node> openSet = new PriorityQueue<>(Comparator.comparingInt(Node::getF)); openSet.add(start); while (!openSet.isEmpty()) { Node current = openSet.poll(); if (current.x == goal.x && current.y == goal.y) { return reconstructPath(current); } visited[current.x][current.y] = true; for (Node neighbor : getNeighbors(current)) { if (visited[neighbor.x][neighbor.y]) continue; openSet.add(neighbor); } } return Collections.emptyList(); // No path found } private List<Node> getNeighbors(Node current) { // Implementation omitted for brevity return new ArrayList<>(); } private List<Node> reconstructPath(Node current) { List<Node> path = new ArrayList<>(); while (current != null) { path.add(current); current = current.parent; } Collections.reverse(path); return path; } } ``` I've tried debugging the heuristic calculations, ensuring the cost from the start node is correct, and even logging the states of the nodes being evaluated during the run. My heuristic function computes the Manhattan distance like this: ```java int manhattanDistance(Node a, Node b) { return Math.abs(a.x - b.x) + Math.abs(a.y - b.y); } ``` However, when I run the algorithm with obstacles at (2, 1) and (3, 1) while trying to navigate to (4, 4), it occasionally fails to find the shortest path. Sometimes it chooses a longer route through (0, 1) instead of going down along the left edge. Is there something wrong with how I'm handling the priority queue, or is my heuristic calculation flawed? Any advice or insights would be greatly appreciated! I'm working on a CLI tool that needs to handle this. Any ideas what could be causing this? I'm working in a Linux environment. Am I missing something obvious?