Minimum Add to Make Parentheses Valid

Problem

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 (Java)

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();
    }
}

Explain:

nope.

Complexity:

Time complexity : O(n).
Space complexity : O(n).