org.apache.lucene.util.Selector.java Source code

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Here is the source code for org.apache.lucene.util.Selector.java

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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.lucene.util;

/** An implementation of a selection algorithm, ie. computing the k-th greatest
 *  value from a collection. */
public abstract class Selector {

    /** Reorder elements so that the element at position {@code k} is the same
     *  as if all elements were sorted and all other elements are partitioned
     *  around it: {@code [from, k)} only contains elements that are less than
     *  or equal to {@code k} and {@code (k, to)} only contains elements that
     *  are greater than or equal to {@code k}. */
    public abstract void select(int from, int to, int k);

    void checkArgs(int from, int to, int k) {
        if (k < from) {
            throw new IllegalArgumentException("k must be >= from");
        }
        if (k >= to) {
            throw new IllegalArgumentException("k must be < to");
        }
    }

    /** Swap values at slots <code>i</code> and <code>j</code>. */
    protected abstract void swap(int i, int j);
}