Find the Shared Letters between Two Strings

Given two strings, return a string containing only the letters shared between the two.

Examples

shared_letters("house", "home") ➞ "eho"

shared_letters("Micky", "mouse") ➞ "m"

shared_letters("house", "villa") ➞ ""

Notes

• If none of the letters are shared, return an empty string.
• The function should be case insensitive (e.g. comparing A and a should return a).
• Sort the resulting string alphabetically before returning it.