There is a circle of red and blue tiles. You are given an array of integers colors and an integer k. The color of tile i is represented by colors[i]: An alternating group is every k contiguous tiles in the circle with alternating colors (each tile in the group except the first and last one has a different color from its left and right tiles). Return the number of alternating groups. Note that since colors represents a circle, the first and the last tiles are considered to be next to each other.