Walmart

Find the length of the longest substring within a given string that contains no repeating characters. The substring must be contiguous.

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.

Determine if a string containing parentheses is valid. A valid string has matching and properly nested opening and closing parentheses.