Determine if you can escape a maze with obstacles, given a starting point and a target. The maze is very large, so a simple search may not be efficient.

You are given a grid representing land and water. Find the water cell that is furthest from any land cell, and return the distance. If the grid is all land or all water, return -1.

You're given a sequence of numbers, each belonging to one of three groups. Find the minimum number of operations to sort the sequence so that all numbers from the same group are clustered together.