Address Leiden numbering issue

cpp/src/community/leiden_impl.cuh

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022-2024, NVIDIA CORPORATION.
+ * Copyright (c) 2022-2025, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -713,6 +713,57 @@ std::pair<size_t, weight_t> leiden(
 
   detail::flatten_leiden_dendrogram(handle, graph_view, *dendrogram, clustering);
 
+  // Get unique cluster id
+  size_t local_num_verts = (*dendrogram).get_level_size_nocheck(0);
+  rmm::device_uvector<vertex_t> unique_cluster_ids(local_num_verts, handle.get_stream());
+
+  thrust::copy(handle.get_thrust_policy(),
+               clustering,
+               clustering + local_num_verts,
+               unique_cluster_ids.begin());
+
+  thrust::sort(handle.get_thrust_policy(), unique_cluster_ids.begin(), unique_cluster_ids.end());
+
+  unique_cluster_ids.resize(thrust::distance(unique_cluster_ids.begin(),
+                                             thrust::unique(handle.get_thrust_policy(),
+                                                            unique_cluster_ids.begin(),
+                                                            unique_cluster_ids.end())),
+                            handle.get_stream());
+
+  if constexpr (multi_gpu) {
+    auto recvcounts = cugraph::host_scalar_allgather(
+      handle.get_comms(), unique_cluster_ids.size(), handle.get_stream());
+
+    std::vector<size_t> displacements(recvcounts.size());
+    std::exclusive_scan(recvcounts.begin(), recvcounts.end(), displacements.begin(), size_t{0});
+    rmm::device_uvector<vertex_t> allgathered_unique_cluster_ids(
+      displacements.back() + recvcounts.back(), handle.get_stream());
+    cugraph::device_allgatherv(handle.get_comms(),
+                               unique_cluster_ids.begin(),
+                               allgathered_unique_cluster_ids.begin(),
+                               recvcounts,
+                               displacements,
+                               handle.get_stream());
+
+    thrust::sort(handle.get_thrust_policy(),
+                 allgathered_unique_cluster_ids.begin(),
+                 allgathered_unique_cluster_ids.end());
+
+    allgathered_unique_cluster_ids.resize(
+      thrust::distance(allgathered_unique_cluster_ids.begin(),
+                       thrust::unique(handle.get_thrust_policy(),
+                                      allgathered_unique_cluster_ids.begin(),
+                                      allgathered_unique_cluster_ids.end())),
+      handle.get_stream());
+
+    detail::relabel_cluster_ids<vertex_t, multi_gpu>(
+      handle, allgathered_unique_cluster_ids, clustering, local_num_verts);
+
+  } else {
+    detail::relabel_cluster_ids<vertex_t, multi_gpu>(
+      handle, unique_cluster_ids, clustering, local_num_verts);
+  }
+
   return std::make_pair(dendrogram->num_levels(), modularity);
 }
 

python/cugraph/cugraph/dask/community/leiden.py

@@ -1,4 +1,4 @@
-# Copyright (c) 2022-2024, NVIDIA CORPORATION.
+# Copyright (c) 2022-2025, NVIDIA CORPORATION.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -156,13 +156,13 @@ def leiden(
             input_graph._plc_graph[w],
             max_iter,
             resolution,
-            random_state,
+            random_state + i,
             theta,
             do_expensive_check,
             workers=[w],
             allow_other_workers=False,
         )
-        for w in Comms.get_workers()
+        for i, w in enumerate(Comms.get_workers())
     ]
 
     wait(result)