com.twitter.graphjet.demo.TopNodes.java Source code

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Here is the source code for com.twitter.graphjet.demo.TopNodes.java

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/**
 * Copyright 2016 Twitter. All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.twitter.graphjet.demo;

import com.google.common.collect.Lists;

import java.util.ArrayList;
import java.util.List;
import java.util.PriorityQueue;

/**
 * Heap for keeping track of top <i>k</i> nodes based on scores.
 */
public class TopNodes {
    private final int k;
    private PriorityQueue<NodeValueEntry> queue;

    /**
     * Creates a heap for keeping track of top <i>k</i> nodes based on scores.
     *
     * @param k number of nodes to keep track of
     */
    public TopNodes(int k) {
        this.k = k;
        this.queue = new PriorityQueue<>(this.k);
    }

    /**
     * Records this node with a particular score if it is in the top <i>k</i>. Otherwise, do nothing.
     * Note that we defer creation of an object until we know the node is in the top <i>k</i> to
     * avoid unnecessary object creation.
     *
     * @param nodeId  node id
     * @param score   score
     */
    public void offer(long nodeId, double score) {
        if (queue.size() < k) {
            queue.add(new NodeValueEntry(nodeId, score));
        } else {
            NodeValueEntry peek = queue.peek();
            if (score > peek.getValue()) {
                queue.poll();
                queue.add(new NodeValueEntry(nodeId, score));
            }
        }
    }

    /**
     * Returns the top <i>k</i> nodes encountered by this heap.
     *
     * @return the top <i>k</i> nodes encountered by this heap.
     */
    public List<NodeValueEntry> getNodes() {
        NodeValueEntry e;
        final List<NodeValueEntry> entries = new ArrayList<>(queue.size());
        while ((e = queue.poll()) != null) {
            entries.add(e);
        }

        return Lists.reverse(entries);
    }
}