CSc $120$: List to String $($Version $2)$

Expected Behavior

Write a function concat$\_$elements$($slist$,$ startpos, stoppos$),$ where slist is a list of strings and startpos and stoppos are integers, that concatenates the elements of slist starting at position startpos and ending at position stoppos $($inclusive$)$ and returns the resulting string.

Your code should behave reasonably for all values of startpos and stoppos: if startpos is negative, concatenation should start with the first element of slist; if stoppos $>=$ len$($slist$),$ concatenation should stop at the last element of slist. If startpos $>$ stoppos it should return the empty string. See the examples below.

Programming Requirements

Solve this problem without explicitly iterating over the list. One way to do this involves a combination of slicing and join$().$

Examples

concat$\_$elements$([\text{'}$aa$\text{'},\text{'}$bb$\text{'},\text{'}$cc$\text{'},\text{'}$dd$\text{'}],1,3)$

return value: $\text{'}$bbccdd$\text{'}$

concat$\_$elements$([\text{'}$aa$\text{'},\text{'}$bb$\text{'},\text{'}$cc$\text{'},\text{'}$dd$\text{'}],-1,1)$

return value: 'aabb'

concat$\_$elements$([\text{'}$aa$\text{'},\text{'}$bb$\text{'},\text{'}$cc$\text{'},\text{'}$dd$\text{'}],-9,9)$

return value: 'aabbccdd'

concat$\_$elements$([\text{'}$aa$\text{'},\text{'}$bb$\text{'},\text{'}$cc$\text{'},\text{'}$dd$\text{'}],3,3)$

return value: $\text{'}$dd$\text{'}$

concat$\_$elements$([\text{'}$aa$\text{'},\text{'}$bb$\text{'},\text{'}$cc$\text{'},\text{'}$dd$\text{'}],3,1)$

return value: $\text{'}\text{'}$