Task
📝 **Task:** Write `next_greater(nums)` returning, for each index, the next greater element to its right (or -1). Print `next_greater([2,1,2,4,3,1])`. Expected: [4, 2, 4, -1, -1, -1]
📋 Edit the starter code. Tests run automatically.
💡 **Hint:** Re-read the theory if stuck.