Functions — *args and **kwargs

Implement solve(mode, *args, **kwargs) that behaves differently based on mode:

• "sum" → return the sum of all positional args (numbers). Return 0 if none.
• "join" → join all positional args as strings with the separator from kwargs.get("sep", " ").
• "merge" → merge all **kwargs into a single dict and return it.

Examples

• solve("sum", 1, 2, 3, 4) → 10
• solve("join", "hello", "world", sep="-") → "hello-world"
• solve("join", "a", "b", "c") → "a b c"
• solve("merge", x=1, y=2, z=3) → {"x": 1, "y": 2, "z": 3}