io.github.deepeshpatel.jnumbertools.generator.permutation.repetitive.RepetitivePermutation Maven / Gradle / Ivy
/*
* JNumberTools Library v1.0.3
* Copyright (c) 2022 Deepesh Patel ([email protected])
*/
package io.github.deepeshpatel.jnumbertools.generator.permutation.repetitive;
import io.github.deepeshpatel.jnumbertools.generator.base.AbstractGenerator;
import java.util.*;
/**
* Utility to generate all permutations of given items and size where items can be repeated.
* Permutations are generated in lexicographical order of indices of input values, considering value at each index as unique.
*
* Instance of this class is intended to be created via builder and hence do not have any public constructor.
* @author Deepesh Patel
*
* @param the type of elements to permute
*/
public final class RepetitivePermutation extends AbstractGenerator {
private final int size;
/**
* Constructs a RepetitivePermutation with the specified elements and size.
*
* @param elements the list of elements to permute
* @param size the size of each permutation. This can be greater than the number of elements due to repetition.
*/
RepetitivePermutation(List elements, int size) {
super(elements);
this.size = size;
}
@Override
public Iterator> iterator() {
return new NumberIterator();
}
private class NumberIterator implements Iterator> {
private final int[] currentIndices = new int[size];
private boolean hasNext = true;
@Override
public boolean hasNext() {
return hasNext;
}
@Override
public List next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
List result = indicesToValues(currentIndices);
hasNext = nextRepetitivePermutation(currentIndices, elements.size());
return result;
}
/**
* Updates the indices array to the next permutation in lexicographical order.
*
* @param indices the current indices
* @param base the size of the base set (number of unique elements)
* @return true if there are more permutations, false if the end is reached
*/
private boolean nextRepetitivePermutation(int[] indices, int base) {
for (int i = 0, j = indices.length - 1; j >= 0; j--, i++) {
if (indices[j] == base - 1) {
indices[j] = 0;
} else {
indices[j]++;
return true;
}
}
return false;
}
}
}