> For the complete documentation index, see [llms.txt](https://garychang.gitbook.io/leetcode/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://garychang.gitbook.io/leetcode/20.-valid-parentheses.md).

# 20. Valid Parentheses

<https://leetcode.com/problems/valid-parentheses/description/>

Given a string containing just the characters `'('`, `')'`, `'{'`, `'}'`, `'['` and `']'`, determine if the input string is valid.

An input string is valid if:

1. Open brackets must be closed by the same type of brackets.
2. Open brackets must be closed in the correct order.

Note that an empty string is also considered valid.

**Example 1:**

```
Input: "()"
Output: true
```

**Example 2:**

```
Input: "()[]{}"
Output: true
```

**Example 3:**

```
Input: "(]"
Output: false
```

**Example 4:**

```
Input: "([)]"
Output: false
```

**Example 5:**

```
Input: "{[]}"
Output: true
```

**Solution:**

```
class Solution(object):
    def isValid(self, s):
        """
        :type s: str
        :rtype: bool
        """
        stack = [None]
        pars = {')': '(', '}': '{', ']': '['}
        for ss in s:
            if ss in pars and pars[ss] == stack[len(stack)-1]:
                stack.pop()
            else:
                stack.append(ss)
        return len(stack) == 1
```