---
title: '20. Valid Parentheses'
description: Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid
icon: dot
topics:
  - { name: "String", slug: "string" }
  - { name: "Stack", slug: "stack" }
  - { name: "Bracket Sequences", slug: "bracket-sequences" }
video: "WTzjTskDFMg"
issue: "https://github.com/prdlk/leetcode/issues/67"
companies:
  - { name: "BlackRock", period: "Thirty Days", frequency: 100 }
  - { name: "Microsoft", period: "Thirty Days", frequency: 67.9 }
  - { name: "Amazon", period: "Thirty Days", frequency: 61.3 }
  - { name: "Google", period: "Thirty Days", frequency: 42.3 }
  - { name: "Accolite", period: "Three Months", frequency: 100 }
  - { name: "Intuit", period: "Three Months", frequency: 73.2 }
  - { name: "Bloomberg", period: "Three Months", frequency: 68.3 }
  - { name: "Meta", period: "Three Months", frequency: 65.3 }
  - { name: "tcs", period: "Three Months", frequency: 57.2 }
  - { name: "Autodesk", period: "Six Months", frequency: 100 }
  - { name: "Criteo", period: "Six Months", frequency: 100 }
  - { name: "Odoo", period: "Six Months", frequency: 100 }
  - { name: "Tripadvisor", period: "Six Months", frequency: 100 }
  - { name: "Virtu Financial", period: "Six Months", frequency: 100 }
  - { name: "IBM", period: "Six Months", frequency: 91.1 }
  - { name: "Epic Systems", period: "Six Months", frequency: 89.6 }
  - { name: "LinkedIn", period: "Six Months", frequency: 85.6 }
sidebar:
  label: 'Valid Parentheses'
  badge: 'Easy'
---

### Example 1:
- Input: `s = "()"`
- Output: `true`

### Example 2:
- Input: `s = "()[]{}"`
- Output: `true`

### Example 3:
- Input: `s = "(]"`
- Output: `false`

### Example 4:
- Input: `s = "([])"`
- Output: `true`

### Example 5:
- Input: `s = "([)]"`
- Output: `false`

### Constraints:

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

## Approach

```mermaid
flowchart TD
  S(["isValid(s)"]) --> I["stack = [], pairs = closer to opener"]
  I --> L{"more char c?"}
  L -- no --> Z{"stack empty?"}
  Z -- yes --> T(["return True"])
  Z -- no --> U(["return False — unclosed openers left"])
  L -- yes --> Q{"c is a closer?"}
  Q -- no --> A["stack.append(c) — it is an opener"]
  A --> L
  Q -- yes --> M{"stack non-empty and pairs[c] == stack[-1]?"}
  M -- yes --> P["stack.pop() — matched"]
  P --> L
  M -- no --> F(["return False — mismatch"])
```

## Solution

```py
class Solution:
    def isValid(self, s: str) -> bool:
        stack = []
        pairs = {")": "(", "]": "[", "}": "{"}

        for c in s:
            if c in pairs:
                if stack and pairs[c] == stack[-1]:
                    stack.pop()
                else:
                    return False
            else:
                stack.append(c)

        return True if not stack else False
```