Sets — Set Operations

Implement solve(a, b, op) where a and b are lists of values and op is one of:

• "union" → elements in a or b (or both)
• "intersection" → elements in both a and b
• "difference" → elements in a but not in b
• "symmetric_difference" → elements in a or b but not both

Return the result as a sorted list (so the output is deterministic).

Examples

• solve([1,2,3], [2,3,4], "union") → [1, 2, 3, 4]
• solve([1,2,3], [2,3,4], "intersection") → [2, 3]
• solve([1,2,3], [2,3,4], "difference") → [1]
• solve([1,2,3], [2,3,4], "symmetric_difference") → [1, 4]