Given a string s that contains parentheses and letters, remove the minimum number of invalid parentheses to make the input string valid.

Return a list of unique strings that are valid with the minimum number of removals. You may return the answer in any order.

  Example 1:

Input: s = "()())()" Output: ["(())()","()()()"]

Example 2:

Input: s = "(a)())()" Output: ["(a())()","(a)()()"]

Example 3:

Input: s = ")(" Output: [""]

  Constraints:

1 <= s.length <= 25
s consists of lowercase English letters and parentheses '(' and ')'.
There will be at most 20 parentheses in s.