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/simplify-path/

Difficulty: Medium

Premium: False

Question

Given a string path, which is an absolute path (starting with a slash '/') to a file or directory in a Unix-style file system, convert it to the simplified canonical path. In a Unix-style file system, a period '.' refers …

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Question Link : https://leetcode.com/problems/removing-stars-from-a-string/

Difficulty: Medium

Premium: False

Question

You are given a string s, which contains stars *. In one operation, you can:

Choose a star in s. Remove the closest non-star character to its left, as well as remove the star itself.

Return the string after …

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Question Link : https://leetcode.com/problems/design-browser-history/

Difficulty: Medium

Premium: False

Question

You have a browser of one tab where you start on the homepage and you can visit another url, get back in the history number of steps or move forward in the history number of steps. Implement the …

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Question Link : https://leetcode.com/problems/implement-queue-using-stacks/

Difficulty: Easy

Premium: False

Question

Implement a first in first out (FIFO) queue using only two stacks. The implemented queue should support all the functions of a normal queue (push, peek, pop, and empty). Implement the MyQueue class:

void push(int x) Pushes …

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Question Link : https://leetcode.com/problems/evaluate-reverse-polish-notation/

Difficulty: Medium

Premium: False

Question

Evaluate the value of an arithmetic expression in Reverse Polish Notation. Valid operators are +, -, *, and /. Each operand may be an integer or another expression. Note that division between two integers should truncate toward zero. It is guaranteed that …

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Question Link : https://leetcode.com/problems/length-of-the-longest-alphabetical-continuous-substring/

Difficulty: Medium

Question

An alphabetical continuous string is a string consisting of consecutive letters in the alphabet. In other words, it is any substring of the string "abcdefghijklmnopqrstuvwxyz".

For example, "abc" is an alphabetical continuous string, while "acb" and "za" are not.

Given …

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Question Link : https://leetcode.com/problems/make-the-string-great/

Difficulty: Easy

Question

Given a string s of lower and upper case English letters. A good string is a string which doesn't have two adjacent characters s[i] and s[i + 1] where:

0 <= i <= s.length - 2 s[i] is a lower-case …

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Question Link : https://leetcode.com/problems/validate-stack-sequences/

Difficulty: Medium

Question

Given two integer arrays pushed and popped each with distinct values, return true if this could have been the result of a sequence of push and pop operations on an initially empty stack, or false otherwise.   Example 1:

Input: pushed …

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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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