Given a string s and a string array dictionary, return the longest string from the dictionary that can be formed by deleting some characters of s. If there are multiple valid words, return the longest word with the smallest lexicographical order. If no valid word exists, return an empty string.
Design a URL shortening system where you can encode a long URL into a shortened URL and decode it back to the original URL. The system should guarantee that the original URL can always be retrieved using the shortened version.
Given a positive integer n, find the smallest integer which can be formed by rearranging the digits of n and is greater than n. If no such integer exists, return -1.
