Determine if it is possible to finish all courses given prerequisite relationships between them. Essentially, detect if a cycle exists in the course dependencies.

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

Determine the fewest modifications needed to transform a binary string into an alternating pattern (e.g., "0101" or "1010"). You can change '0' to '1' or '1' to '0'.