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1249. Minimum Remove to Make Valid Parentheses

Difficulty Topics

Description

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.

Solution

minimum-remove-to-make-valid-parentheses.py
class Solution:
    def minRemoveToMakeValid(self, s: str) -> str:
        n = len(s)
        stack = []
        res = [""] * n

        for i, x in enumerate(s):
            if x == "(":
                stack.append((x, i))
            elif x == ")":
                if stack and stack[-1][0] == "(":
                    ele, index = stack.pop()
                    res[index] = ele
                    res[i] = x
                else:
                    if stack:
                        stack.pop()
            else:
                res[i] = x

        return "".join(res)