# 1249. Minimum Remove to Make Valid Parentheses
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.
Example 4:
Input: s = "(a(b(c)d)"
Output: "a(b(c)d)"
# Solution
Approach 1: stack.
# Code (Python)
Approach 1:
class Solution:
def minRemoveToMakeValid(self, s: str) -> str:
stack = []
for i in range(len(s)):
if s[i] not in ('(', ')'):
continue
if s[i] == '(':
stack.append(i)
else:
if stack and s[stack[-1]] == '(':
stack.pop()
else:
stack.append(i)
stack = set(stack)
result = []
for i in range(len(s)):
if i in stack:
continue
result.append(s[i])
return ''.join(result)
# Code (C++)
Approach 1:
Approach 2: