Greedy Best-First Search

1open.add(new int[]{h(start), start}); queued[start] = true;  // Seed open by heuristic h2while (!open.isEmpty()) {  // Until open set is empty3  int node = open.poll()[1];  // Pop cell closest to goal4  if (visited[node]) continue;  // Skip if already visited5  if (node == goal) return buildPath();  // Goal found — trace path6  visited[node] = true;  // Mark cell visited7  for (int neighbor : neighbors(node))  // Scan passable neighbors8    if (!visited[neighbor] && !queued[neighbor]) {  // Only brand-new cells9      parent[neighbor] = node; queued[neighbor] = true;  // Record parent, mark queued10      open.add(new int[]{h(neighbor), neighbor});  // Queue by h alone11    }12}13 14int h(int cell) {  // Manhattan distance to goal15  int r = cell / COLS, c = cell % COLS;16  int gr = goal / COLS, gc = goal % COLS;17  return Math.abs(r - gr) + Math.abs(c - gc);18}19 20List<Integer> neighbors(int cell) {  // Passable 4-neighbors21  int r = cell / COLS, c = cell % COLS;22  int[][] dirs = {{-1, 0}, {1, 0}, {0, -1}, {0, 1}};23  List<Integer> out = new ArrayList<>();24  for (int[] d : dirs) {25    int nr = r + d[0], nc = c + d[1];26    if (nr < 0 || nr >= ROWS || nc < 0 || nc >= COLS) continue;27    int nbr = nr * COLS + nc;28    if (!walls.contains(nbr)) out.add(nbr);29  }30  return out;31}32 33List<Integer> buildPath() {  // Walk parent back from goal34  List<Integer> path = new ArrayList<>();35  for (int at = goal; at != -1; at = parent[at]) path.add(at);36  Collections.reverse(path);37  return path;38}