Design a data structure that acts as a Least Recently Used (LRU) cache. Implement methods to get and put key-value pairs, evicting the least recently used entry when the cache is full.

Given a string, remove duplicate letters so that each letter appears only once. Ensure the resulting string is the smallest in lexicographical order among all possible results.

Find the lexicographically smallest subsequence of distinct characters from a given string. You need to ensure each character appears only once and the relative order is maintained.