3206. Alternating Groups I

There is a circle of red and blue tiles. You are given an array of integers colors. The color of tile i is represented by colors[i]:

• colors[i] == 0 means that tile i is red.
• colors[i] == 1 means that tile i is blue.

Every 3 contiguous tiles in the circle with alternating colors (the middle tile has a different color from its left and right tiles) is called an alternating group.

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.

class Solution {
public:
    int numberOfAlternatingGroups(vector<int>& A) {
        int res = 0, n = A.size();
        for(int i = 0; i < n; i++) {
            if(A[i] != A[(i+1)%n]) {
                if(A[i] == A[(i+2)%n]) res++;
            }
        }
        return res;
    }
};