Finding the gem (Programming problem)

There is a 5by5 grid where each cell contains a gem. Each gem has a name. The grid should contain only one Kohinoor. Find the Kohinoor. At each step of the search, print the cell name where you are searching. As soon as you find the Kohinoor, stop searching and print Kohinoor is found.

Programming problem (Naive)

A square is given in Cartesian coordinate system. The coordinates of only three points of the square are given. Assume that coordinates have only integer values. Find the forth coordinates.