Need javascript solution of the following problem:

Tom is decorating the pavement in his garden with N square tiles. Each tile is divided into four triangles of different colors (white - 'W', red - 'R', green - 'G' and blue - 'B'). A tile is described as a string of four characters denoting respectively, the color of the upper, right, bottom and left triangle. For example, the tile in the figure below is described as "WRGB".