use rayon::prelude::*;

fn par_swap_remove<T, I>(v: &mut Vec<T>, indices: I)
where
    T: Send + Sync + std::fmt::Display,
    I: IntoParallelIterator<Item = usize>,
    I::Iter: IndexedParallelIterator,
{
    struct SafePtr<T: ?Sized>(*mut T);
    unsafe impl<T: ?Sized> Send for SafePtr<T> {}
    unsafe impl<T: ?Sized> Sync for SafePtr<T> {}

    // Exercise for the reader to validate the incomming parallel iterator

    let len = v.len();
    let ptr = SafePtr(v.as_mut_ptr());

    let removed = indices
        .into_par_iter()
        .enumerate()
        .map(move |(i, idx)| unsafe {
            let SafePtr(ptr) = ptr;

            let hole: *mut _ = ptr.add(idx);
            let last = ptr.add(len - i - 1);
            std::ptr::swap(hole, last);
        })
        .count();

    v.truncate(len - removed);
}

fn main() {
    let mut v = vec![1, 2, 3, 4, 5];
    let indices: Vec<usize> = vec![0, 2, 4];
    par_swap_remove(&mut v, indices);
    println!("{:?}", v);
}