Given a string ~s~ of lower and upper case English letters.
A good string is a string which doesn't have *two adjacent characters*~s[i]~ and ~s[i + 1]~ where:
- ~0 <= i <= s.length - 2~
- ~s[i]~ is a lower-case letter and ~s[i + 1]~ is the same letter but in upper-case or *vice-versa*.
To make the string good, you can choose *two adjacent* characters that make the string bad and remove them. You can keep doing this until the string becomes good.
Return /the string/ after making it good. The answer is guaranteed to be unique under the given constraints.
*Notice* that an empty string is also good.
*Example 1:*
#+begin_src
Input: s = "leEeetcode"
Output: "leetcode"
Explanation: In the first step, either you choose i = 1 or i = 2, both will result "leEeetcode" to be reduced to "leetcode".
#+end_src
*Example 2:*
#+begin_src
Input: s = "abBAcC"
Output: ""
Explanation: We have many possible scenarios, and all lead to the same answer. For example:
"abBAcC" --> "aAcC" --> "cC" --> ""
"abBAcC" --> "abBA" --> "aA" --> ""
#+end_src
*Example 3:*
#+begin_src
Input: s = "s"
Output: "s"
#+end_src
*Constraints:*
- ~1 <= s.length <= 100~
- ~s~ contains only lower and upper case English letters.