Uncommons Maths API
(Version 1.2.3)

## org.uncommons.maths.combinatorics Class CombinationGenerator<T>

```java.lang.Object
org.uncommons.maths.combinatorics.CombinationGenerator<T>
```
Type Parameters:
`T` - The type of element that the combinations are made from.
All Implemented Interfaces:
Iterable<List<T>>

`public class CombinationGenerator<T>extends Objectimplements Iterable<List<T>>`

Combination generator for generating all combinations of a given size from the specified set of elements. For performance reasons, this implementation is restricted to operating with set sizes and combination lengths that produce no more than 2^63 different combinations.

Author:
Daniel Dyer (modified from the original version written by Michael Gilleland of Merriam Park Software - http://www.merriampark.com/comb.htm).
`PermutationGenerator`

Constructor Summary
```CombinationGenerator(Collection<T> elements, int combinationLength)```
Create a combination generator that generates all combinations of a specified length from the given set.
```CombinationGenerator(T[] elements, int combinationLength)```
Create a combination generator that generates all combinations of a specified length from the given set.

Method Summary
` long` `getRemainingCombinations()`

` long` `getTotalCombinations()`

` boolean` `hasMore()`
Are there more combinations?
` Iterator<List<T>>` `iterator()`
Provides a read-only iterator for iterating over the combinations generated by this object.
` T[]` `nextCombinationAsArray()`
Generate the next combination and return an array containing the appropriate elements.
` T[]` `nextCombinationAsArray(T[] destination)`
Generate the next combination and return an array containing the appropriate elements.
` List<T>` `nextCombinationAsList()`
Generate the next combination and return a list containing the appropriate elements.
` List<T>` `nextCombinationAsList(List<T> destination)`
Generate the next combination and return a list containing the appropriate elements.
` void` `reset()`
Reset the combination generator.

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

### CombinationGenerator

```public CombinationGenerator(T[] elements,
int combinationLength)```
Create a combination generator that generates all combinations of a specified length from the given set.

Parameters:
`elements` - The set from which to generate combinations.
`combinationLength` - The length of the combinations to be generated.

### CombinationGenerator

```public CombinationGenerator(Collection<T> elements,
int combinationLength)```
Create a combination generator that generates all combinations of a specified length from the given set.

Parameters:
`elements` - The set from which to generate combinations.
`combinationLength` - The length of the combinations to be generated.
Method Detail

### reset

`public final void reset()`
Reset the combination generator.

### getRemainingCombinations

`public long getRemainingCombinations()`
Returns:
The number of combinations not yet generated.

### hasMore

`public boolean hasMore()`
Are there more combinations?

Returns:
true if there are more combinations available, false otherwise.

### getTotalCombinations

`public long getTotalCombinations()`
Returns:
The total number of combinations.

### nextCombinationAsArray

`public T[] nextCombinationAsArray()`
Generate the next combination and return an array containing the appropriate elements.

Returns:
An array containing the elements that make up the next combination.
`nextCombinationAsArray(Object[])`, `nextCombinationAsList()`

### nextCombinationAsArray

`public T[] nextCombinationAsArray(T[] destination)`
Generate the next combination and return an array containing the appropriate elements. This overloaded method allows the caller to provide an array that will be used and returned. The purpose of this is to improve performance when iterating over combinations. If the `nextCombinationAsArray()` method is used it will create a new array every time. When iterating over combinations this will result in lots of short-lived objects that have to be garbage collected. This method allows a single array instance to be reused in such circumstances.

Parameters:
`destination` - Provides an array to use to create the combination. The specified array must be the same length as a combination.
Returns:
The provided array now containing the elements of the combination.

### nextCombinationAsList

`public List<T> nextCombinationAsList()`
Generate the next combination and return a list containing the appropriate elements.

Returns:
A list containing the elements that make up the next combination.
`nextCombinationAsList(List)`, `nextCombinationAsArray()`

### nextCombinationAsList

`public List<T> nextCombinationAsList(List<T> destination)`
Generate the next combination and return a list containing the appropriate elements. This overloaded method allows the caller to provide a list that will be used and returned. The purpose of this is to improve performance when iterating over combinations. If the `nextCombinationAsList()` method is used it will create a new list every time. When iterating over combinations this will result in lots of short-lived objects that have to be garbage collected. This method allows a single list instance to be reused in such circumstances.

Parameters:
`destination` - Provides a list to use to create the combination.
Returns:
The provided list now containing the elements of the combination.

### iterator

`public Iterator<List<T>> iterator()`

Provides a read-only iterator for iterating over the combinations generated by this object. This method is the implementation of the `Iterable` interface that permits instances of this class to be used with the new-style for loop.

For example:

``` List<Integer> elements = Arrays.asList(1, 2, 3);
CombinationGenerator<Integer> combinations = new CombinationGenerator(elements, 2);
for (List<Integer> c : combinations)
{
// Do something with each combination.
}
```

Specified by:
`iterator` in interface `Iterable<List<T>>`
Returns:
An iterator.
Since:
1.1

Uncommons Maths API
(Version 1.2.3)