colour debug template

// colout print
template <class T1, class T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) {
  return os << '{' << p.first << ", " << p.second << '}';
}

template <class T, class = decltype(begin(declval<T>())),
          class = enable_if_t<!is_same<T, string>::value>>
ostream &operator<<(ostream &os, const T &c) {
  os << '[';
  for (auto it = begin(c); it != end(c); ++it)
    os << (it == begin(c) ? "" : ", ") << *it;
  return os << ']';
}

#define _NTH_ARG(_1, _2, _3, _4, _5, _6, N, ...) N
#define _FE_1(_CALL, x) _CALL(x)
#define _FE_2(_CALL, x, ...) _CALL(x) _FE_1(_CALL, __VA_ARGS__)
#define _FE_3(_CALL, x, ...) _CALL(x) _FE_2(_CALL, __VA_ARGS__)
#define _FE_4(_CALL, x, ...) _CALL(x) _FE_3(_CALL, __VA_ARGS__)
#define _FE_5(_CALL, x, ...) _CALL(x) _FE_4(_CALL, __VA_ARGS__)
#define _FE_6(_CALL, x, ...) _CALL(x) _FE_5(_CALL, __VA_ARGS__)
#define FOR_EACH_MACRO(MACRO, ...)                                             \
  _NTH_ARG(__VA_ARGS__, _FE_6, _FE_5, _FE_4, _FE_3, _FE_2, _FE_1)              \
  (MACRO, __VA_ARGS__)
#define watch(x) cerr << "\033[1;32m" #x " = \033[1;34m" << (x) << "\033[0m; ";
#define dbg(...)                                                             \
  cerr << "\033[2;31mLine " << __LINE__ << ": \033[0;m";                       \
  FOR_EACH_MACRO(watch, __VA_ARGS__)                                           \
  cerr << "\n"