921. Minimum Add to Make Parentheses Valid

Posted on Edited on In

921. Minimum Add to Make Parentheses Valid

Description

A parentheses string is valid if and only if:

  • It is the empty string,
  • 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.

You are given a parentheses string s. In one move, you can insert a parenthesis at any position of the string.

  • For example, if s = "()))", you can insert an opening parenthesis to be "(**(** )))" or a closing parenthesis to be "())**)** )".

Return the minimum number of moves required to make s valid.

Example 1:

1
2
Input: s = "())"
Output: 1

Example 2:

1
2
Input: s = "((("
Output: 3

Constraints:

  • 1 <= s.length <= 1000
  • s[i] is either '(' or ')'.

Hints/Notes

Solution

Language: C++

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
class Solution {
public:
    int minAddToMakeValid(string s) {
        int left = 0, res = 0;
        for (auto& c : s) {
            if (c == '(') {
                left++;
            } else if (c == ')') {
                if (!left) {
                    res++;
                } else {
                    left--;
                }
            }
        }
        res += left;
        return res;
    }
};