Given a 2D grid, each cell is either a zombie `1` or a human `0`. Zombies can turn adjacent (up/down/left/right) human beings into zombies every hour. Find out how many hours does it take to infect all humans?\n\n**Example:**\n```\nInput:\n[[0, 1, 1, 0, 1],\n [0, 1, 0, 1, 0],\n [0, 0, 0, 0, 1],\n [0, 1, 0, 0, 0]]\n\nOutput: 2\n\nExplanation:\nAt the end of the 1st hour, the status of the grid:\n[[1, 1, 1, 1, 1],\n [1, 1, 1, 1, 1],\n [0, 1, 0, 1, 1],\n [1, 1, 1, 0, 1]]\n\nAt the end of the 2nd hour, the status of the grid:\n[[1, 1, 1, 1, 1],\n [1, 1, 1, 1, 1],\n [1, 1, 1, 1, 1],\n [1, 1, 1, 1, 1]]\n```\n\n```java\nint minHours(int rows, int columns, List<List<Integer>> grid) {\n\t// todo\n}\n```\n-----------\nRelated problems:\n* https://leetcode.com/problems/rotting-oranges/\n* https://leetcode.com/problems/walls-and-gates/ (premium)

Given a 2D grid, each cell is either a zombie 1 or a human 0. Zombies can turn adjacent (up/down/left/right) human beings into zombies every hour. Find out how 