Question Link : https://leetcode.com/problems/valid-parentheses/

Difficulty: Easy

Premium: False

Question

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 …

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Question Link : https://leetcode.com/problems/basic-calculator/

Difficulty: Hard

Question

Given a string s representing a valid expression, implement a basic calculator to evaluate it, and return the result of the evaluation. Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions, such as …

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Question Link : https://leetcode.com/problems/minimum-remove-to-make-valid-parentheses/

Difficulty: Medium

Question

Given a string s of '(' , ')' and lowercase English characters. Your task is to remove the minimum number of parentheses ( '(' or ')', in any positions ) so that the resulting parentheses string is valid and return any valid string. Formally, a parentheses string …

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