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Fix String


Given a string, s, containing only '(' , ')' and lowercase English characters.

Your task is to fix the string. A string is fixed by removing the minimum number of parentheses ( '(' or ')', in any positions ) so that the resulting parentheses string is valid.


  1. It is the emp...

isPalindrome (Stack/Queue implementation)


Write the function isPalindrome that takes a string as input and outputs whether the string is a palindrome or not. Implement this function using a stack or a queue (although if you cannot, you can do it using for/while loops). Examples of palindromes are:


You ca...

Minimum Add to Make Parentheses Valid


Given a string S of '(' and ')' parentheses, we add the minimum number of parentheses ( '(' or ')', and in any positions ) so that the resulting parentheses string is valid.

Formally, a parentheses string is valid if and only if:

  • It is the empty string, or
  • It can be written as AB (A concaten...

Reverse Array using Stacks or Queues


Hello! Reversing an array is pretty simple right? Make a for loop, add some stuff to a new array and you're done! But what if I told you there were an easier way?!?! Issa Stack or Queue So yeah, I want you to reverse an array using only a Stack or a Queue, you will be given a populated array of len...

Teemo Attacks!


In League of Legends there is a character named Teemo who can poison his enemies. Given Teemo's attacking ascending time series towards his opponent and the poisoning time duration per Teemo's attacking, you need to output the total time that his opponent is in poisoned condition.

You may assume...

Valid Parentheses


Given a string containing just the characters '(', ')', '{', '}', '[', ']', 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.

Input: "()" Output: true

Input: "(...