last-survivors-ep-dot-2

Last Survivors Ep.2

Substitute two equal letters by the next letter of the alphabet (two letters convert to one):

"aa" => "b", "bb" => "c", .. "zz" => "a".

The equal letters do not have to be adjacent.
Repeat this operation until there are no possible substitutions left.
Return a string.

Example:

let str = "zzzab"
    str = "azab"
    str = "bzb"
    str = "cz"
return "cz"

Notes

• The order of letters in the result is not important.
• The letters "zz" transform into "a".
• There will only be lowercase letters.