Language: C++

/**
 *    author  : 𝒌𝒚𝒐𝒎𝒖𝒌𝒚𝒐𝒎𝒖𝒑𝒖𝒓𝒊𝒏
 *    created : 2019-12-08 03:41:06
**/

#include <iostream>
#include <deque>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
#include <algorithm>
#include <cmath>
#include <complex>
#include <numeric>
#include <bitset>
#include <cassert>
#include <cctype>
#include <functional>
#include <iomanip>
#include <random>
#include <utility>

using namespace std;

using int64 = long long;
#define debug(_) cerr << #_ << ": " << (_) << '\n'
template<class T> ostream& operator<<(ostream& os, vector<T>& _) { os << '{'; for (T& x : _) { os << x; if (&x != &_.back()) os << ','; } os << '}'; return os; }
template<class T, class U> ostream& operator<<(ostream& os, pair<T, U>& p) { return os << '{' << p.first << " " << p.second << '}'; }

template <typename T>
class Modular {
 public:
  using Type = typename decay<decltype(T::value)>::type;
 
  constexpr Modular() : value() {}
  template <typename U>
  Modular(const U& x) {
    value = normalize(x);
  }
 
  template <typename U>
  static Type normalize(const U& x) {
    Type v;
    if (-mod() <= x && x < mod()) v = static_cast<Type>(x);
    else v = static_cast<Type>(x % mod());
    if (v < 0) v += mod();
    return v;
  }
 
  const Type& operator()() const { return value; }
  template <typename U>
  explicit operator U() const { return static_cast<U>(value); }
  constexpr static Type mod() { return T::value; }
 
  Modular& operator+=(const Modular& other) { if ((value += other.value) >= mod()) value -= mod(); return *this; }
  Modular& operator-=(const Modular& other) { if ((value -= other.value) < 0) value += mod(); return *this; }
  template <typename U> Modular& operator+=(const U& other) { return *this += Modular(other); }
  template <typename U> Modular& operator-=(const U& other) { return *this -= Modular(other); }
  Modular& operator++() { return *this += 1; }
  Modular& operator--() { return *this -= 1; }
  Modular operator++(int) { Modular result(*this); *this += 1; return result; }
  Modular operator--(int) { Modular result(*this); *this -= 1; return result; }
  Modular operator-() const { return Modular(-value); }
 
  template <typename U = T>
  typename enable_if<is_same<typename Modular<U>::Type, int>::value, Modular>::type& operator*=(const Modular& rhs) {
#ifdef _WIN32
    uint64_t x = static_cast<int64_t>(value) * static_cast<int64_t>(rhs.value);
    uint32_t xh = static_cast<uint32_t>(x >> 32), xl = static_cast<uint32_t>(x), d, m;
    asm(
      "divl %4; \n\t"
      : "=a" (d), "=d" (m)
      : "d" (xh), "a" (xl), "r" (mod())
    );
    value = m;
#else
    value = normalize(static_cast<int64_t>(value) * static_cast<int64_t>(rhs.value));
#endif
    return *this;
  }
  template <typename U = T>
  typename enable_if<is_same<typename Modular<U>::Type, int64_t>::value, Modular>::type& operator*=(const Modular& rhs) {
    int64_t q = static_cast<int64_t>(static_cast<long double>(value) * rhs.value / mod());
    value = normalize(value * rhs.value - q * mod());
    return *this;
  }
  template <typename U = T>
  typename enable_if<!is_integral<typename Modular<U>::Type>::value, Modular>::type& operator*=(const Modular& rhs) {
    value = normalize(value * rhs.value);
    return *this;
  }
 
  Modular& operator/=(const Modular& other) { return *this *= Modular(inverse(other.value, mod())); }
 
  template <typename U>
  friend const Modular<U>& abs(const Modular<U>& v) { return v; }
 
  template <typename U>
  friend bool operator==(const Modular<U>& lhs, const Modular<U>& rhs);
 
  template <typename U>
  friend bool operator<(const Modular<U>& lhs, const Modular<U>& rhs);
 
  template <typename U>
  friend std::istream& operator>>(std::istream& stream, Modular<U>& number);
 
 private:
  Type value;
};
 
template <typename T> bool operator==(const Modular<T>& lhs, const Modular<T>& rhs) { return lhs.value == rhs.value; }
template <typename T, typename U> bool operator==(const Modular<T>& lhs, U rhs) { return lhs == Modular<T>(rhs); }
template <typename T, typename U> bool operator==(U lhs, const Modular<T>& rhs) { return Modular<T>(lhs) == rhs; }
 
template <typename T> bool operator!=(const Modular<T>& lhs, const Modular<T>& rhs) { return !(lhs == rhs); }
template <typename T, typename U> bool operator!=(const Modular<T>& lhs, U rhs) { return !(lhs == rhs); }
template <typename T, typename U> bool operator!=(U lhs, const Modular<T>& rhs) { return !(lhs == rhs); }
 
template <typename T> bool operator<(const Modular<T>& lhs, const Modular<T>& rhs) { return lhs.value < rhs.value; }
 
template <typename T> Modular<T> operator+(const Modular<T>& lhs, const Modular<T>& rhs) { return Modular<T>(lhs) += rhs; }
template <typename T, typename U> Modular<T> operator+(const Modular<T>& lhs, U rhs) { return Modular<T>(lhs) += rhs; }
template <typename T, typename U> Modular<T> operator+(U lhs, const Modular<T>& rhs) { return Modular<T>(lhs) += rhs; }
 
template <typename T> Modular<T> operator-(const Modular<T>& lhs, const Modular<T>& rhs) { return Modular<T>(lhs) -= rhs; }
template <typename T, typename U> Modular<T> operator-(const Modular<T>& lhs, U rhs) { return Modular<T>(lhs) -= rhs; }
template <typename T, typename U> Modular<T> operator-(U lhs, const Modular<T>& rhs) { return Modular<T>(lhs) -= rhs; }
 
template <typename T> Modular<T> operator*(const Modular<T>& lhs, const Modular<T>& rhs) { return Modular<T>(lhs) *= rhs; }
template <typename T, typename U> Modular<T> operator*(const Modular<T>& lhs, U rhs) { return Modular<T>(lhs) *= rhs; }
template <typename T, typename U> Modular<T> operator*(U lhs, const Modular<T>& rhs) { return Modular<T>(lhs) *= rhs; }
 
template <typename T> Modular<T> operator/(const Modular<T>& lhs, const Modular<T>& rhs) { return Modular<T>(lhs) /= rhs; }
template <typename T, typename U> Modular<T> operator/(const Modular<T>& lhs, U rhs) { return Modular<T>(lhs) /= rhs; }
template <typename T, typename U> Modular<T> operator/(U lhs, const Modular<T>& rhs) { return Modular<T>(lhs) /= rhs; }
 
template<typename T, typename U>
Modular<T> power(const Modular<T>& a, const U& b) {
  assert(b >= 0);
  Modular<T> x = a, res = 1;
  U p = b;
  while (p > 0) {
    if (p & 1) res *= x;
    x *= x;
    p >>= 1;
  }
  return res;
}
 
template <typename T>
bool IsZero(const Modular<T>& number) {
  return number() == 0;
}
 
template <typename T>
string to_string(const Modular<T>& number) {
  return to_string(number());
}
 
template <typename T>
std::ostream& operator<<(std::ostream& stream, const Modular<T>& number) {
  return stream << number();
}
 
template <typename T>
std::istream& operator>>(std::istream& stream, Modular<T>& number) {
  typename common_type<typename Modular<T>::Type, int64_t>::type x;
  stream >> x;
  number.value = Modular<T>::normalize(x);
  return stream;
}
 
/*
using ModType = int;
 
struct VarMod { static ModType value; };
ModType VarMod::value;
ModType& md = VarMod::value;
using Mint = Modular<VarMod>;
*/
 
constexpr int md = 1e9 + 7;
using Mint = Modular<std::integral_constant<decay<decltype(md)>::type, md>>;

template<typename T> T mod_pow(int x, int n) {
  Mint res = 1;
  while (n > 0) {
    if (n & 1) res *= x;
    x *= x;
    n >>= 1;
  }
  return res;
}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);

  string s; cin >> s;
  int n = s.size();
  vector<int> cntA(n, 0), cntB(n, 0), cntC(n, 0), cntq(n, 0);

  for (int i = 0; i < n; ++i) {
    cntA[i] = s[i] == 'A';
    cntB[i] = s[i] == 'B';
    cntC[i] = s[i] == 'C';
    cntq[i] = s[i] == '?';
  }
 
  for (int i = 1; i < n; ++i) {
    cntA[i] += cntA[i - 1];
    cntB[i] += cntB[i - 1];
    cntC[i] += cntC[i - 1];
    cntq[i] += cntq[i - 1];
  }

  Mint ans = 0;  for (int i = 1; i < n - 1; ++i) {
    if (s[i] == 'A' || s[i] == 'C') continue;
    Mint left = cntA[i - 1] * mod_pow<Mint>(3, cntq[i - 1]) + cntq[i - 1] * mod_pow<Mint>(3, cntq[i - 1] - 1);
    Mint right = (cntC[n - 1] - cntC[i]) * mod_pow<Mint>(3, cntq[n - 1] - cntq[i]) + (cntq[n - 1] - cntq[i]) * mod_pow<Mint>(3, cntq[n - 1] - cntq[i] - 1);
    ans += left * right;
  }

  assert((Mint)0 <= ans && ans < (Mint)md);
  cout << ans << endl;

  return 0;
}


Compiler output:
In file included from /usr/include/c++/14/cassert:44,
                 from a.cc:19:
a.cc: In function 'int main()':
a.cc:227:18: error: no match for 'operator<=' (operand types are 'Mint' {aka 'Modular<std::integral_constant<int, 1000000007> >'} and 'Mint' {aka 'Modular<std::integral_constant<int, 1000000007> >'})
  227 |   assert((Mint)0 <= ans && ans < (Mint)md);
      |          ~~~~~~~ ^~ ~~~
      |          |          |
      |          |          Modular<[...]>
      |          Modular<[...]>
In file included from /usr/include/c++/14/string:48,
                 from /usr/include/c++/14/bits/locale_classes.h:40,
                 from /usr/include/c++/14/bits/ios_base.h:41,
                 from /usr/include/c++/14/ios:44,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:6:
/usr/include/c++/14/bits/stl_iterator.h:469:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator<=(const reverse_iterator<_Iterator>&, const reverse_iterator<_Iterator>&)'
  469 |     operator<=(const reverse_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:469:5: note:   template argument deduction/substitution failed:
a.cc:227:21: note:   'Mint' {aka 'Modular<std::integral_constant<int, 1000000007> >'} is not derived from 'const std::reverse_iterator<_Iterator>'
  227 |   assert((Mint)0 <= ans && ans < (Mint)md);
      |                     ^~~
/usr/include/c++/14/bits/stl_iterator.h:513:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator<=(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  513 |     operator<=(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:513:5: note:   template argument deduction/substitution failed:
a.cc:227:21: note:   'Mint' {aka 'Modular<std::integral_constant<int, 1000000007> >'} is not derived from 'const std::reverse_iterator<_Iterator>'
  227 |   assert((Mint)0 <= ans && ans < (Mint)md);
      |                     ^~~
/usr/include/c++/14/bits/stl_iterator.h:1704:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator<=(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1704 |     operator<=(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1704:5: note:   template argument deduction/substitution failed:
a.cc:227:21: note:   'Mint' {aka 'Modular<std::integral_constant<int, 1000000007> >'} is not derived from 'const std::move_iterator<_IteratorL>'
  227 |   assert((Mint)0 <= ans && ans < (Mint)md);
      |                     ^~~
/usr/include/c++/14/bits/stl_iterator.h:1767:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator<=(const move_iterator<_IteratorL>&, const move_iterator<_IteratorL>&)'
 1767 |     operator<=(const move_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1767:5: note:   template argument deduction/substitution failed:
a.cc:227:21: note:   'Mint' {aka 'Modular<std::integral_constant<int, 1000000007> >'} is not derived from 'const std::move_iterator<_IteratorL>'
  227 |   assert((Mint)0 <= ans && ans < (Mint)md);
      |                     ^~~
In file included from /usr/include/c++/14/bits/stl_algobase.h:64,
                 from /usr/include/c++/14/string:51:
/usr/include/c++/14/bits/stl_pair.h:1064:5: note: candidate: 'template<class _T1, class _T2> constexpr bool std::operator<=(const pair<_T1, _T2>&, const pair<_T1, _T2>&)'
 1064 |     operator<=(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:1064:5: note:   template argument deduction/substitution failed:
a.cc:227:21: note:   'Mint' {aka 'Modular<std::integral_constant<int, 1000000007> >'} is not derived from 'const std::pair<_T1, _T2>'
  227 |   assert((Mint)0 <= ans && ans < (Mint)md);
      |                     ^~~
In file included from /usr/include/c++/14/bits/basic_string.h:47,
                 from /usr/include/c++/14/string:54:
/usr/include/c++/14/string_view:717:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator<=(basic_string_view<_CharT, _Traits>, basic_string_view<_CharT, _Traits>)'
  717 |     operator<=(basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:717:5: note:   template argument deduction/substitution failed:
a.cc:227:21: note:   'Modular<std::integral_constant<int, 1000000007> >' is not derived from 'std::basic_string_view<_CharT, _Traits>'
  227 |   assert((Mint)0 <= ans && ans < (Mint)md);
      |                     ^~~
/usr/include/c++/14/string_view:724:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator<=(basic_string_view<_CharT, _Traits>, __type_identity_t<basic_string_view<_CharT, _Traits> >)'
  724 |     operator<=(basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:724:5: note:   template argument deduction/substitution failed:
a.cc:227:21: note:   'Modular<std::integral_constant<int, 1000000007> >' is not derived from 'std::basic_string_view<_CharT, _Traits>'
  227 |   assert((Mint)0 <= ans && ans < (Mint)md);
      |                     ^~~
/usr/include/c++/14/string_view:732:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator<=(__type_identity_t<basic_string_view<_CharT, _Traits> >, basic_string_view<_CharT, _Traits>)'
  732 |     operator<=(__type_identity_t<basic_string_view<_CharT, _Traits>> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:732:5: note:   template argument deduction/substitution failed:
a.cc:227:21: note:   'Modular<std::integral_constant<int, 1000000007> >' is not derived from 'std::basic_string_view<_CharT, _Traits>'
  227 |   assert((Mint)0 <= ans && ans < (Mint)md);
      |                     ^~~
/usr/include/c++/14/bits/basic_string.h:3956:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator<=(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3956 |     operator<=(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3956:5: note:   template argument deduction/substitution failed:
a.cc:227:21: note:   'Mint' {aka 'Modular<std::integral_constant<int, 1000000007> >'} is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
  227 |   assert((Mint)0 <= ans && ans < (Mint)md);
      |                     ^~~
/usr/include/c++/14/bits/basic_string.h:3970:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator<=(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const _CharT*)'
 3970 |     operator<=(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3970:5: note:   template argument deduction/substitution failed:
a.cc:227:21: note:   'Mint' {aka 'Modular<std::integral_constant<int, 1000000007> >'} is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
  227 |   assert((Mint)0 <= ans && ans < (Mint)md);
      |                     ^~~
/usr/include/c++/14/bits/basic_string.h:3983:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator<=(const _CharT*, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3983 |     operator<=(const _CharT* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3983:5: note:   template argument deduction/substitution failed:
a.cc:227:21: note:   mismatched types 'const _CharT*' and 'Modular<std::integral_constant<int, 1000000007> >'
  227 |   assert((Mint)0 <= ans && ans < (Mint)md);
      |                     ^~~
In file included from /usr/include/c++/14/bits/memory_resource.h:47,
                 from /usr/include/c++/14/string:68:
/usr/include/c++/14/tuple:2625:5: note: candidate: 'template<class ... _TElements, class ... _UElements> constexpr bool std::operator<=(const tuple<_UTypes ...>&, const tuple<_Elements ...>&)'
 2625 |     operator<=(const tuple<_TElements...>& __t,
      |     ^~~~~~~~
/usr/include/c++/14/tuple:2625:5: note:   template argument deduction/substitution failed:
a.cc:227:21: note:   'Mint' {aka 'Modular<std::integral_constant<int, 1000000007> >'} is not derived from 'const std::tuple<_UTypes ...>'
  227 |   assert((Mint)0 <= ans && ans < (Mint)md);
      |                     ^~~
In file included from /usr/include/c++/14/deque:66,
                 from a.cc:7:
/usr/include/c++/14/bits/stl_deque.h:2356:5: note: candidate: 'template<class _Tp, class _Alloc> bool std::operator<=(const deque<_Tp, _Alloc>&, const deque<_Tp, _Alloc>&)'
 2356 |     operator<=(const deque<_Tp, _Alloc>& __x, const deque<_Tp, _Alloc>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_deque.h:2356:5: note:   template argument deduction/substitution failed:
a.cc:227:21: note:   'Mint' {aka 'Modular<std::integral_constant<int, 1000000007> >'} is not derived from 'const std::deque<_Tp, _Alloc>'
  227 |   assert((Mint)0 <= ans && ans < (Mint)md);
      |                     ^~~
In file included from /usr/include/c++/14/map:63,
                 from a.cc:8:
/usr/include/c++/14/bits/stl_map.h:1571:5: note: candidate: 'template<class _Key, class _Tp, class _Compare, class _Alloc> bool std::operator<=(const map<_Key, _Tp, _Compare, _Allocator>&, const map<_Key, _Tp, _Compare, _Allocator>&)'
 1571 |     operator<=(const map<_Key, _Tp, _Compare, _Alloc>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_map.h:1571:5: note:   template argument deduction/substitution failed:
a.cc:227:21: note:   'Mint' {aka 'Modular<std::integral_constant<int, 1000000007> >'} is not derived from 'const std::map<_Key, _Tp, _Compare, _Allocator>'
  227 |   assert((Mint)0 <= ans && ans < (Mint)md);
      |                     ^~~
In file included from /usr/include/c++/14/map:64:
/usr/include/c++/14/bits/stl_multimap.h:1193:5: note: can