LeetCode-in-Java

921. Minimum Add to Make Parentheses Valid

Medium

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:

Input: s = “())”

Output: 1

Example 2:

Input: s = “(((“

Output: 3

Constraints:

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

Solution

import java.util.ArrayDeque;
import java.util.Deque;

@SuppressWarnings("java:S1149")
public class Solution {
    public int minAddToMakeValid(String s) {
        Deque<Character> stack = new ArrayDeque<>();
        for (char c : s.toCharArray()) {
            if (c == ')') {
                if (!stack.isEmpty() && stack.peek() == '(') {
                    stack.pop();
                } else {
                    stack.push(c);
                }
            } else {
                stack.push(c);
            }
        }
        return stack.size();
    }
}

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