Created
October 10, 2020 00:47
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Combinations in Rust
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fn comb<T>(slice: &[T], k: usize) -> Vec<Vec<T>> | |
where | |
T: Copy, | |
{ | |
// If k == 1, return a vector containing a vector for each element of the slice. | |
if k == 1 { | |
return slice.iter().map(|x| vec![*x]).collect::<Vec<Vec<T>>>(); | |
} | |
// If k is exactly the slice length, return the slice inside a vector. | |
if k == slice.len() { | |
return vec![slice.to_vec()]; | |
} | |
// Make a vector from the first element + all combinations of k - 1 elements of the rest of the slice. | |
let mut result = comb(&slice[1..], k - 1) | |
.into_iter() | |
.map(|x| [&slice[..1], x.as_slice()].concat()) | |
.collect::<Vec<Vec<T>>>(); | |
// Extend this last vector with the all the combinations of k elements after from index 1 onward. | |
result.extend(comb(&slice[1..], k)); | |
// Return final vector. | |
return result; | |
} |
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