Spelling Bee Valid Words Finder

bloomberg Spelling Bee Game In the Spelling Bee game, you need to list all words that satisfy the following rules: The word must be at least 4 letters long. The required letter must appear at least once. Optional letters can appear any number of times (repeats allowed). No other letters are allowed. For example, with N as the required letter and V, C, O, D, E, Y as optional letters, valid words include: ENCODE, NONCE, DONE, NODE. Please write a function to complete this task and provide test cases. Example Input required = 'O', optionals = ['G', 'L', 'E', 'P', 'T', 'N'], dictionary = {'POLE', 'TONE', 'TOLL', 'GONE', 'NOTE', 'TOGG', 'ONG', 'TROPEN', 'LENTO', 'LOPE'}