Letter Tile Possibilities
Try to solve the Letter Tile Possibilities problem.
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Statement
You are given a string, tiles, consisting of uppercase English letters. You can arrange the tiles into sequences of any length (from 1 to the length of tiles), and each sequence must include at most one tile, tiles[i], from tiles.
Your task is to return the number of possible non-empty unique sequences you can make using the letters represented on tiles[i]. ...