#![allow(unused_variables)]
fn main() {
    let vec = vec![13usize; 1024];
    let _ = vec
        .into_iter()
        .enumerate()
        .filter_map(|(idx, val)| if idx % 2 == 0 { Some(val + idx) } else { None })
        .collect::<Vec<_>>();
    let mut vec = vec![13usize; 1024];
    let mut write_idx = 0;
    for idx in 0..vec.len() {
        if idx % 2 == 0 {
            vec[write_idx] = vec[idx] + idx;
            write_idx += 1;
        }
    }
    vec.truncate(write_idx);
}