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use std::collections::HashSet;
pub struct Subset<'a, T> {
set: &'a [T],
idxs: &'a [usize]
}
pub struct SubsetIterator<'a, T> {
subset: &'a Subset<'a, T>,
iter: std::slice::Iter<'a, usize>
}
#[derive(Debug,PartialEq,Eq)]
pub enum IndexError {
NotUnique,
OutOfBounds
}
impl<'a, T> Subset<'a, T> {
pub fn new(set: &'a [T], idxs: &'a [usize]) -> Result<Self, IndexError> {
let set_size = set.len();
let uniques: HashSet<usize> = idxs.iter().map(|v| *v).collect();
if uniques.len() < idxs.len() {
Err(IndexError::NotUnique)
} else if idxs.iter().any(|v| *v >= set_size) {
Err(IndexError::OutOfBounds)
} else { Ok(unsafe{Self::new_unchecked(set, idxs)}) }
}
pub unsafe fn new_unchecked(set: &'a [T], idxs: &'a [usize]) -> Self {
Self {
set: set,
idxs: idxs
}
}
pub fn iter(&'a self) -> SubsetIterator<'a, T> {
SubsetIterator {
subset: self,
iter: self.idxs.iter()
}
}
}
impl<'a, T> Iterator for SubsetIterator<'a, T> {
type Item = &'a T;
fn next(&mut self) -> Option<&'a T> {
self.iter.next().map(|v| &self.subset.set[*v])
}
}
impl<'a, T> DoubleEndedIterator for SubsetIterator<'a, T> {
fn next_back(&mut self) -> Option<&'a T> {
self.iter.next_back().map(|v| &self.subset.set[*v])
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_set() {
let set = vec![9, 8, 7, 6, 5, 4, 3, 2, 1, 0];
let idxs = vec![2, 2];
assert_eq!(Subset::new(&set, &idxs).err(), Some(IndexError::NotUnique));
let idxs = vec![10];
assert_eq!(Subset::new(&set, &idxs).err(), Some(IndexError::OutOfBounds));
let idxs = vec![2, 4, 7];
let subset = Subset::new(&set, &idxs).unwrap();
let mut sum = 0;
for e in subset.iter() {
sum += e;
}
assert_eq!(sum, 14);
let mut sum = 0;
for e in subset.iter().map(|v| 2*v).rev() {
sum += e;
}
assert_eq!(sum, 28);
}
}