Leetcode 0231. Power of Two
Given an integer `n`, return `true` if it is a power of two. Otherwise, return `false`. An integer `n` is a power of two, if there exists an integer `x` such that `n == 2x`. Example...
Paolography
Leetcode 0933. Number of Recent Calls
You have a `RecentCounter` class which counts the number of recent requests within a certain time frame. Implement the `RecentCounter` class: - `RecentCounter()` Initializes the coun...
Leetcode 0232. Implement Queue using Stacks
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...
Leetcode 0155. Min Stack
Design a stack that supports push, pop, top, and retrieving the minimum element in constant time. Implement the `MinStack` class: - `MinStack()` initializes the stack object. - `vo...
Leetcode 0020. 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...
Leetcode 0203. Remove Linked List Elements
Given the `head` of a linked list and an integer `val`, remove all the nodes of the linked list that has `Node.val == val`, and return the new head. Example 1: Input: head = [1,2,6...
Leetcode 0141. Linked List Cycle
Given `head`, the head of a linked list, determine if the linked list has a cycle in it. There is a cycle in a linked list if there is some node in the list that can be reached again by c...
Leetcode 0021. Merge Two Sorted Lists
You are given the heads of two sorted linked lists `list1` and `list2`. Merge the two lists in a one sorted list. The list should be made by splicing together the nodes of the first two l...
Leetcode 0125. Valid Palindrome
A phrase is a palindrome if, after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters, it reads the same forward and backward. Alphanumeric ch...
Leetcode 0344. Reverse String
Write a function that reverses a string. The input string is given as an array of characters `s`. You must do this by modifying the input array in-place with `O(1)` extra memory. Ex...