Create a function that takes two lowercase strings str1 and str2 of letters from a to z and returns the sorted and longest string containing distinct letters.
str1 = "mubashir"
str2 = "detabi"
longestString(str1, str2) ➞ "abdehimrstu"
// Contains sorted and distinct letters of the given strings.
str1 = "abcdefghijklmnopqrstuvwxyz"
str2 = "abcdefghijklmnopqrstuvwxyz"
longestString(str1, str2) ➞ "abcdefghijklmnopqrstuvwxyz"
// Contains sorted and distinct letters of the given strings.
N/A