What alghorithm can i use to find the biggest subarray within a 2d array with only n different numbers

First off i am sorry if this is the wrong place to post this.

Let me try to explain my problem lets say i have a 2d array 100x100 in size each cell in that array has a number from 1 to 50 randomly. How do i find the biggest subarray in a ractangle size in that array that has only n diffrent numbers.

Small example:

array: 1 2 3 3 3 2 2
       7 4 3 3 4 9 8
       1 2 3 3 3 4 2
       7 6 1 9 9 4 2
In this case the biggest sub rectangle with only 1 number allowed would be 
       3 3
       3 3
With 2 numbers allowed it would be
       3 3 3
       3 3 4
       3 3 3

Does a something for this exist?