> ## Documentation Index
> Fetch the complete documentation index at: https://leetcode-py.wisl.dev/llms.txt
> Use this file to discover all available pages before exploring further.

> ## Agent Instructions
> leetcode-py is a Python LeetCode practice environment generator with one CLI: lcpy. It is not a service or platform.
> Each problem is a directory under leetcode/ with README.md, solution.py, test_solution.py, helpers.py, and playground.ipynb. lcpy gen creates them from JSON templates bundled with the package.
> Examples are backed by tests; copy them verbatim.

# Valid Parentheses Python Solution with Tests

> Tested Python solution for LeetCode 20 with 20 pytest cases. Generate a practice environment with lcpy.

LeetCode 20, Easy. Topics: String, Stack. [View on LeetCode](https://leetcode.com/problems/valid-parentheses/description/).

Generate this problem as a practice environment: tested reference solution, 20 [parametrized pytest cases](/practice/testing), and a playground notebook:

```bash theme={"theme":{"light":"github-light","dark":"github-dark"}}
lcpy gen -n 20   # by problem number
lcpy gen -s valid_parentheses   # by problem name
```

## Problem

Given a string `s` 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.
3. Every close bracket has a corresponding open bracket of the same type.

### Examples

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

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

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

```
Input: s = "([])"
Output: true
```

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

### Constraints

* `1 <= s.length <= 10^4`
* `s` consists of parentheses only `'()[]{}'`.

## Solution

Reference implementation from [solution.py on GitHub](https://github.com/wislertt/leetcode-py/blob/main/leetcode/valid_parentheses/solution.py), full suite in [test\_solution.py](https://github.com/wislertt/leetcode-py/blob/main/leetcode/valid_parentheses/test_solution.py):

```python theme={"theme":{"light":"github-light","dark":"github-dark"}}
class Solution:
    # Time: O(n)
    # Space: O(n)
    def is_valid(self, s: str) -> bool:
        stack = []
        pairs = {"(": ")", "[": "]", "{": "}"}

        for char in s:
            if char in pairs:
                stack.append(char)
            elif not stack or pairs[stack.pop()] != char:
                return False

        return not stack
```

## Complexity

| Time | Space |
| ---- | ----- |
| O(n) | O(n)  |

## Tags

[Grind 75](/catalog/grind-75), [Grind](/catalog/grind), [Blind 75](/catalog/blind-75), [NeetCode 150](/catalog/neetcode-150), [NeetCode 250](/catalog/neetcode-250), [NeetCode All](/catalog/neetcode), [AlgoMaster 75](/catalog/algo-master-75).