Problem Statement
An anagram of a string is any string that contains the same characters in any order. For example, the anagrams of "tree" are, in alphabetical order: "eert", "eetr", "eret", "erte", "eter", "etre", "reet", "rete", "rtee", "teer", "tere" and "tree".
You will be given a String s and an int i. Return the ith (0-based) anagram of s when listed in alphabetical order. If there is no such anagram, return an empty String.