Implement Employee Validation and Snake

This interview covered two coding tasks: 1. **Employee validation** - Implement a function that validates a collection of employees against a set of business rules. - Each employee can have direct reports, so validation must recursively process all descendants. - Follow-up: extend the validation so it detects cycles in the reporting structure, for example when employee A indirectly reports back to employee A. 2. **Snake game** - Implement a simplified Snake game on a 2D grid. - The game should handle keyboard input for up, down, left, and right movement. - It should detect wall collisions. - When the snake eats an apple, its length should increase by 1.