对N条数据进行索引，如果N<10, 请问使用哪种结构会更快些？

pub struct Key(String, usize);

pub struct Keys1(Vec<Key>);

pub struct Keys2(HashMap<String, usize>)

pub trait Indexer {
   fn get_index(&self, key_name: &String) -> usize;
}

impl Indexer for Keys1 {
   fn get_index(&self, key_name: &String) -> usize{
     todo!()
   }
}

impl Indexer for Keys2 {
   fn get_index(&self, key_name: &String) -> usize{
     todo!()
   }
}