Simulate a single-threaded CPU processing tasks with varying arrival times and processing durations. Determine the order in which the CPU processes the tasks to minimize idle time, and return the processing order.

Imagine a grid representing rooms, some empty, some with walls, and some with gates. Fill each empty room with the distance to its nearest gate.

Find the longest path in a matrix where each step increases in value. You can only move up, down, left, or right.