Given a string, make a new one following a zig-zag pattern. This means it will take the first letter, the last, the second, second to last, until there aren’t any letters left in the original string.
For example:
zig_zag("apple")→'aeplp'zig_zag("string")→'sgtnri'zig_zag("codingbat")→'ctoadbign'