# [leetcode] 20. Valid Parentheses _ Algorithm Problem Solve for python

## 1. Problem

20. Valid Parentheses

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

An input string is valid if:

Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order. Every close bracket has a corresponding open bracket of the same type.

Example 1:

Input: s = "()"
Output: true


Example 2:

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


Example 3:

Input: s = "(]"
Output: false


Constraints:

• 1 <= s.length <= 104
• s consists of parentheses only ‘()[]{}’.

## 2. Solution

I solve this problem like this.

• Using stack and dictionary.
• It loops through the for string and checks each word one by one.
• If character is in ‘([{‘, push stack.
• If character is not in ‘([{‘, check stack’s top value is pair of brackets.
class Solution:
def isValid(self, s: str) -> bool:
stack = []
for _s in s:
if _s in '([{':
stack.append(_s)
continue

dic = {'(': ')', '[': ']', '{': '}'}

if len(stack) > 0 and dic.get(stack[-1], None) == _s:
stack.pop()
continue
else:
return False

return True if len(stack) == 0 else False