public static int birthday(List<Integer> s, int d, int m) {
        int count = 0;   // current sum of the window
        int steps = 0;   // current window size
        int total = 0;   // total valid segments

        for (int i = 0; i < s.size(); i++) {
            steps++;
            count += s.get(i);

            if (steps == m) {
                if (count == d) {
                    total++;
                }

                // Instead of resetting, slide the window
                count -= s.get(i - m + 1); // remove oldest element
                steps--;                   // shrink window by 1
            }
        }
        return total;
    }