Struct permutator::GosperCombination

pub struct GosperCombination<'a, T>where
    T: 'a,{ /* private fields */ }

Create a combination iterator. It use Gosper’s algorithm to pick a combination out of given data. The produced combination provide no lexicographic order.

The returned combination will be a reference into given data. Each combination return from iterator will be a new Vec. It’s safe to hold onto a combination or collect it.

Examples

Given slice of [1, 2, 3, 4, 5]. It will produce following combinations: [1, 2, 3], [1, 2, 4], [1, 3, 4], [2, 3, 4], [1, 2, 5], [1, 3, 5], [2, 3, 5], [1, 4, 5], [2, 4, 5], [3, 4, 5]

   use permutator::GosperCombination;
   use std::time::{Instant};
   let gosper = GosperCombination::new(&[1, 2, 3, 4, 5], 3);
   let mut counter = 0;
   let timer = Instant::now();

   for combination in gosper {
       // uncomment a line below to print each combination
       // println!("{}:{:?}", counter, combination);
       counter += 1;
   }

   println!("Total {} combinations in {:?}", counter, timer.elapsed());

Limitation

Gosper algorithm need to know the MSB (most significant bit). The current largest known MSB data type is u128. This make the implementation support up to 128 elements slice.

See

• Gospel’s algorithm in Wikipedia page, October 9, 2018

Implementations

impl<'a, T> GosperCombination<'a, T>

pub fn new(data: &[T], r: usize) -> GosperCombination<'_, T>

Create new combination generator using Gosper’s algorithm. r shall be smaller than data.len().

Note: It perform no check on given parameter. If r is larger than length of data then iterate over it will not occur. The iteration will be end upon enter.

pub fn len(&self) -> usize

Total number of combinations this iterate can return. It will equals to n!/((n-r)!*r!)

pub fn next(&mut self, result: &mut [&'a T]) -> Option<()>

Attempt to get next combination and mutate a given result to store the next combination. This function mimic Iterator’s next style. It’ll return an empty Option because result will be contain in given paramter. It return None when there’s no further possible combination.

pub fn next_into_cell(
    &mut self,
    result: &Rc<RefCell<&mut [&'a T]>>
) -> Option<()>

Attempt to get next combination and store it into Rc<RefCell<>> of mutable slice result to store the next combination. This function mimic Iterator’s next style. It’ll return an empty Option because result will be contain in given paramter. It return None when there’s no further possible combination.

Use this function when you want a faster than copy/clone but need to share the combination to multiple target.

The test in uncontrol environment found that using this function yield performance on par with combination_cell function.

Trait Implementations

impl<'a, T> IntoIterator for GosperCombination<'a, T>

type Item = Vec<&'a T, Global>

The type of the elements being iterated over.

type IntoIter = CombinationIterator<'a, T>

Which kind of iterator are we turning this into?

fn into_iter(self) -> CombinationIterator<'a, T>

Creates an iterator from a value.