Today I have done leetcode's February LeetCoding Challenge with cpp.

February LeetCoding Challenge 19

Description

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)"

Constraints:

• 1 <= s.length <= 10^5
• s[i] is one of '(' , ')' and lowercase English letters.

Solution

class Solution {
public:
    string minRemoveToMakeValid(string s) {
        int len = s.length();
        
        vector<int> st;
        for(int i = 0; i < len; ++i) {
            if(s[i] == ')') {
                if(st.size()) st.pop_back();
                else s[i] = 0;
            } else if(s[i] == '(') st.push_back(i);
        }
        while(st.size()) {
            s[st.back()] = 0;
            st.pop_back();
        }
        
        string answer;
        for(auto c : s) if(c) answer.push_back(c);
        return answer;
    }
};