content: /**
   * 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.apex.examples.machinedata.util;
  
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  
  /**
   * Generate combinations of elements for the given array of elements.
   *
   * Implements nCr = n! / (r! * (n-r)!)
   *
   * @since 0.3.5
   */
  public class Combinatorics<T>
  {
  
    private T[] values;
    private int size = -1;
    private List<T> result;
    private Map<Integer, List<T>> resultMap = new HashMap<Integer, List<T>>();
    private int resultMapSize = 0;
  
    /**
     * Generates all possible combinations with all the sizes.
     *
     * @param values
     */
    public Combinatorics(T[] values)
    {
      this.values = values;
      this.size = -1;
      this.result = new ArrayList<>();
    }
  
    /**
     * Generates all possible combinations with the given size.
     *
     * @param values
     * @param size
     */
    public Combinatorics(T[] values, int size)
    {
      this.values = values;
      this.size = size;
      this.result = new ArrayList<>();
    }
  
    public Map<Integer, List<T>> generate()
    {
  
      if (size == -1) {
        size = values.length;
        for (int i = 1; i <= size; i++) {
          int[] tmp = new int[i];
          Arrays.fill(tmp, -1);
          generateCombinations(0, 0, tmp);
        }
      } else {
        int[] tmp = new int[size];
        Arrays.fill(tmp, -1);
        generateCombinations(0, 0, tmp);
      }
      return resultMap;
    }
  
    public void generateCombinations(int start, int depth, int[] tmp)
    {
      if (depth == tmp.length) {
        for (int j = 0; j < depth; j++) {
          result.add(values[tmp[j]]);
        }
        resultMap.put(++resultMapSize, result);
        result = new ArrayList<>();
        return;
      }
      for (int i = start; i < values.length; i++) {
        tmp[depth] = i;
        generateCombinations(i + 1, depth + 1, tmp);
      }
    }
  }
  