#Graph Algorithms

You have a grid of oranges where some are rotten and some are fresh. Every minute, any fresh orange that is adjacent to a rotten orange becomes rotten. Given the grid, return the minimum number of minutes that must elapse until no cell has a fresh orange. If it is impossible, return -1. Example: Input: grid = [[2,1,1],[1,1,0],[0,1,1]] Output: 4.