Minimum_remove_to_make_valid_parentheses.py

"""
Given a string s of '(' , ')' and lowercase English characters.

Your task is to remove the minimum number of parentheses ( '(' or ')', in any positions ) so that the resulting parentheses string is valid and return any valid string.

Formally, a parentheses string is valid if and only if:

It is the empty string, contains only lowercase characters, or
It can be written as AB (A concatenated with B), where A and B are valid strings, or
It can be written as (A), where A is a valid string.
 

Example 1:

Input: s = "lee(t(c)o)de)"
Output: "lee(t(c)o)de"
Explanation: "lee(t(co)de)" , "lee(t(c)ode)" would also be accepted.
Example 2:

Input: s = "a)b(c)d"
Output: "ab(c)d"
Example 3:

Input: s = "))(("
Output: ""
Explanation: An empty string is also valid.
 

Constraints:

1 <= s.length <= 105
s[i] is either '(' , ')', or lowercase English letter.

"""

class Solution:
    def minRemoveToMakeValid(self, s: str) -> str:
        stack = []

        for i, char in enumerate(s):
            if char =='(':
                stack.append(i)
            elif char ==')':
                if stack and s[stack[-1]] == '(':
                    stack.pop()
                else:
                    stack.append(i)
        result = []
        for i, char in enumerate(s):
            if stack and i == stack[0]:
                stack.pop(0)
                continue
            result.append(char)
        
        return ''.join(result)