Compute minimum escape time in a grid

You are given a 2D floor plan grid. Each cell is one of: - `.` empty space (walkable) - `#` wall/blocked (not walkable) - `P` a person - `E` an exit A person can move 1 step per minute to the 4-neighbors (up/down/left/right) through walkable cells. Multiple people can occupy the same cell at the same time (ignore collisions). Task: 1) Determine whether **every** person can reach **some** exit. 2) If everyone can escape, return the **minimum time until all people have escaped**, assuming each person walks optimally (i.e., the maximum over people of their shortest-path distance to any exit). If some person cannot reach any exit, return `-1`. Explain an algorithm and its time/space complexity.