1249. Minimum Remove to Make Valid Parentheses

Problem Link

Description

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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

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Python3

class Solution:
    def minRemoveToMakeValid(self, s: str) -> str:
        N = len(s)
        res = [""] * N
        stack = []
 
        for i, x in enumerate(s):
            if x == "(":
                stack.append(i)
            elif x == ")":
                if stack and s[stack[-1]] == "(":
                    j = stack.pop()
                    res[j] = s[j]
                    res[i] = x
            else:
                res[i] = x
 
        return "".join(res)