added trimtosize and fixed a spot where we should be returning KMeansResult

Author: john-wagster

server/src/main/java/org/elasticsearch/index/codec/vectors/DefaultIVFVectorsWriter.java

@@ -291,6 +291,7 @@ CentroidAssignments calculateAndWriteCentroids(
                 }
             }
 
+            cluster.trimToSize();
             assignmentsByCluster[c] = cluster;
         }
 

server/src/main/java/org/elasticsearch/index/codec/vectors/cluster/HierarchicalKMeans.java

@@ -51,7 +51,7 @@ public HierarchicalKMeans(int dimension) {
      * @return the centroids and the vectors assignments and SOAR (spilled from nearby neighborhoods) assignments
      * @throws IOException is thrown if vectors is inaccessible
      */
-    public KMeansIntermediate cluster(FloatVectorValues vectors, int targetSize) throws IOException {
+    public KMeansResult cluster(FloatVectorValues vectors, int targetSize) throws IOException {
 
         if (vectors.size() == 0) {
             return new KMeansIntermediate();

server/src/test/java/org/elasticsearch/index/codec/vectors/cluster/HierarchicalKMeansTests.java

@@ -30,7 +30,7 @@ public void testHKmeans() throws IOException {
         int targetSize = (int) ((float) nVectors / (float) nClusters);
         HierarchicalKMeans hkmeans = new HierarchicalKMeans(dims, maxIterations, sampleSize, clustersPerNeighborhood, soarLambda);
 
-        KMeansIntermediate result = hkmeans.cluster(vectors, targetSize);
+        KMeansResult result = hkmeans.cluster(vectors, targetSize);
 
         float[][] centroids = result.centroids();
         int[] assignments = result.assignments();