I have a very long `lst` containing unique elements. I want to design a function which takes a list of elements as the input and it can return a list of index efficiently. We assume the items needed to find their index are all in the `lst`.

Here is an example:

```
lst = ['ab','sd','ef','de']
items_to_find = ['sd', 'ef', 'sd']
>>> fo(lst, items_to_find)  
# Output: [1,2,1]

```

I have one solution of my own, but it looks less efficient.

```
>> [lst.index(x) for x in items_to_find]

```

Because the `lst` is very long, I need a very fast algorithm to solve it.