README.md

20. Valid Parentheses

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 

Solutions (Python)

1. Remove Valid Parentheses by Stack

classSolution: defisValid(self, s: str) ->bool: iflen(s) %2!=0: returnFalsebrackets= {')': '(', '}': '{', ']': '['} stack= [] forcins: ifcinbracketsandstackandstack[-1] ==brackets[c]: stack.pop() else: stack.append(c) returnnotstack

2. Remove Valid Parentheses from String

classSolution: defisValid(self, s: str) ->bool: whiles.count("()") ors.count("[]") ors.count("{}"): s=s.replace("()", "") s=s.replace("[]", "") s=s.replace("{}", "") returnnots