New consecutive_find. More efficient

consecutive_find.cpp

int consecutive_find(vector<int> arr, int n) {
    for (size_t s = 0, e = 0; e < arr.size(); s = e) {
        while (e < arr.size() && arr[s] == arr[e]) {
            e++;
        }
        if (e - s == (size_t)n) {
            return s;
        }
    }
    return -1;
}