Write a function that returns true if all the strings in an array can be formed by using only the characters from the longest string.
canForm(["mast", "manifest", "met", "fan"]) ➞ true
canForm(["may", "master", "same", "reams"]) ➞ false
canForm(["may", "same", "reams", "mastery"]) ➞ true
There will only be one unique longest string.