Given an array of integers, return indices of the two numbers such that they add up to a specific target.

Given two strings s and t, return true if t is an anagram of s, and false otherwise.

Given an array of strings strs, group the anagrams together. You can return the answer in any order.

Given an integer array nums and an integer k, return the k most frequent elements.

Determine if a 9x9 Sudoku board is valid.

Write a program to solve a Sudoku puzzle by filling the empty cells. A sudoku solution must satisfy all of the following rules: Each of the digits 1-9 must occur exactly once in each row, column, and 3x3 sub-box.

Design a data structure that follows the constraints of a Least Recently Used (LRU) cache. Implement the LRUCache class with get(key) returning the value or -1 if not found, and put(key, value) to insert or update. When capacity is exceeded, evict the least recently used key.

You are given an array of variable pairs equations and an array of real numbers values, where equations[i] = [Ai, Bi] and values[i] represent the equation Ai / Bi = values[i]. Each Ai or Bi is a string that represents a single variable. You are also given some queries, where queries[j] = [Cj, Dj] represents the jth query where you must find the answer for Cj / Dj = ?. Return the answers to all queries.

Given an array routes where routes[i] is a bus route that the ith bus repeats forever. You start at bus stop source and want to go to bus stop target. Return the least number of buses you must take to travel from source to target, or -1 if impossible.

Given an array of meeting time intervals consisting of start and end times [[s1,e1],[s2,e2],...] (si < ei), find the minimum number of conference rooms required.

Design an algorithm to serialize and deserialize a binary tree. There is no restriction on how your serialization/deserialization algorithm should work.