3208. Alternating Groups II

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]:

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

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.

class Solution {
public:
    int numberOfAlternatingGroups(vector<int>& A, int k) {
        int res = 0, n = A.size();
        for(int i = 0; i < k - 1; i++) A.push_back(A[i]);
        int l = 0, r = 0;
        while(l < n) {
            int fl = A[l];
            while(r < A.size() and A[r] == fl) {
                r++;
                fl = !fl;
            }
            res += max(0,(r - l + 1) - k);
            l = r;
        }
        return res;
    }
};