org.paukov.combinatorics3.IntegerPartitionIterator Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of combinatoricslib3 Show documentation

Simple java library to generate permutations, combinations and other combinatorial sequences

The newest version!

/*
  Combinatorics Library 3
  Copyright 2009-2016 Dmytro Paukov [email protected]
 */
package org.paukov.combinatorics3;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

class IntegerPartitionIterator implements Iterator> {

  private final InternalVector vector1;
  private final InternalVector vector2;
  private List currentPartition = null;
  private long currentIndex = 0;
  private int stopIndex = 1; //it should be 0 to stop the iteration.

  IntegerPartitionIterator(IntegerPartitionGenerator generator) {
    if (generator.value > 0) {
      vector1 = new InternalVector(generator.value, 0, 0, generator.value);
      vector2 = new InternalVector(generator.value, 0, generator.value + 1, 1);
    } else {
      stopIndex = 0;
      vector1 = new InternalVector(1, 0, 0, 0);
      vector2 = new InternalVector(1, 0, 0, 0);
    }
  }

  @Override
  public boolean hasNext() {
    return stopIndex != 0;
  }


  @Override
  public List next() {
    this.currentIndex++;
    this.currentPartition = createPartition(stopIndex, vector1, vector2);

    int sum = vector1.get(stopIndex) * vector2.get(stopIndex);
    if (vector1.get(stopIndex) == 1) {
      stopIndex--;
      sum += vector1.get(stopIndex) * vector2.get(stopIndex);
    }

    if (vector2.get(stopIndex - 1) == vector2.get(stopIndex) + 1) {
      stopIndex--;
      vector1.set(stopIndex, vector1.get(stopIndex) + 1);
    } else {
      vector2.set(stopIndex, vector2.get(stopIndex) + 1);
      vector1.set(stopIndex, 1);
    }

    if (sum > vector2.get(stopIndex)) {
      vector2.set(stopIndex + 1, 1);
      vector1.set(stopIndex + 1, sum - vector2.get(stopIndex));
      stopIndex++;
    }

    return currentPartition;
  }

  private static List createPartition(int index, InternalVector vector1,
      InternalVector vector) {
    List partition = new ArrayList<>();
    for (int i = 1; i <= index; i++) {
      for (int j = 0; j < vector1.get(i); j++) {
        partition.add(vector.get(i));
      }
    }
    return partition;
  }

  @Override
  public void remove() {
    throw new UnsupportedOperationException();
  }

  @Override
  public String toString() {
    return "IntegerPartitionIterator=[#" + currentIndex + ", " + currentPartition + "]";
  }

  private static class InternalVector {

    final int[] array;

    InternalVector(int size, int value0, int value1, int value2) {
      array = new int[size + 2];
      array[0] = value0;
      array[1] = value1;
      array[2] = value2;
    }

    int get(int index) {
      return array[index + 1];
    }

    void set(int index, int value) {
      array[index + 1] = value;
    }
  }
}