# Leetcode - Minimum Add to Make Parentheses Valid Solution

Given a string `S`

of `'('`

and `')'`

parentheses, we add the minimum number of parentheses ( `'('`

or `')'`

, and in any positions ) so that the resulting parentheses string is valid.

Formally, a parentheses string is valid if and only if:

- It is the empty string, 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.

Given a parentheses string, return the minimum number of parentheses we must add to make the resulting string valid.

**Example 1:**

```
Input: "())"
Output: 1
```

**Example 2:**

```
Input: "((("
Output: 3
```

**Example 3:**

```
Input: "()"
Output: 0
```

**Example 4:**

```
Input: "()))(("
Output: 4
```

**Note:**

`S.length <= 1000`

`S`

only consists of`'('`

and`')'`

characters.

## Solution in Python

```
class Solution:
def minAddToMakeValid(self, S: str) -> int:
stack = []
for i in S:
if i == "(" or not stack:
stack.append(i)
elif i == ")" and stack[-1]== "(":
stack.pop()
else:
stack.append(i)
return len(stack)
```