Language: C

/**
 *    author:  math2do
 *    created: 12.04.2020 17:41:36
**/

#include <bits/stdc++.h>

using namespace std;

template <typename A, typename B>
string to_string(pair<A, B> p);
 
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);
 
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);
 
string to_string(const string& s) {
  return '"' + s + '"';
}
 
string to_string(const char* s) {
  return to_string((string) s);
}
 
string to_string(bool b) {
  return (b ? "1" : "0");
}
string to_string(const char &ch) {
  return string(1, ch);
}
 
string to_string(vector<bool> v) {
  bool first = true;
  string res = "{";
  for (int i = 0; i < static_cast<int>(v.size()); i++) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(v[i]);
  }
  res += "}";
  return res;
}
 
template <size_t N>
string to_string(bitset<N> v) {
  string res = "";
  for (size_t i = 0; i < N; i++) {
    res += static_cast<char>('0' + v[i]);
  }
  reverse(res.begin(), res.end());
  return res;
}

template <typename A>
string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}
 
template <typename A, typename B>
string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
 
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ")";
}
 
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}

void debug_out() { cerr << endl; }
 
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}
 
#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  #ifdef LOCAL
    freopen("sol.in", "rt", stdin);
  #endif
  int n;
  cin >> n;
  string s;
  cin >> s;
  long long ans = 0;
  vector <int> r(n, 0);
  vector <int> g(n, 0);
  vector <int> b(n, 0);
  for (int i = 0; i < n; i++) {
    r[i] = (s[i] == 'R');
    g[i] = (s[i] == 'G');
    b[i] = (s[i] == 'B');
  } 
  auto cum = [&](vector <int> &arr) {
    for (int i = 1; i < n; i++) {
      arr[i] += arr[i - 1];
    } 
  };
  cum(r);
  cum(g);
  cum(b);

  auto get = [&](vector <int> &arr, int i, int j) {
    int H = arr[j];
    int L = (i - 1 >= 0 ? arr[i - 1] : 0);
    return H - L;
  };

  //debug(s);
  //debug(r);
  //debug(g);
  //debug(b);


  auto find = [&](char f, char m, char e) {
    for (int i = 0; i <= n - 3; i++) {
      for (int j = n - 1; j >= i + 2; j--) {
        if (s[i] == f && s[j] == e) {
          if (m == 'R') {
            int ret = get(r, i, j);
            ans += ret;
          } else if (m == 'G') {
            int ret = get(g, i, j);
            ans += ret;
          } else {
            int ret = get(b, i, j);
            ans += ret;
          } 
          int len = j - i + 1;
          if (len & 1) {
            int pos = i + len / 2;
            ans -= (s[pos] == m);
          }
        } 
      } 
    } 
  };
  find('R', 'G', 'B');
  find('B', 'G', 'R');
  find('R', 'B', 'G');
  find('G', 'B', 'R');
  find('G', 'R', 'B');
  find('B', 'R', 'G');  

  cout << ans << endl;
  return 0;
}


Compiler output:
main.c:6:10: fatal error: bits/stdc++.h: No such file or directory
    6 | #include <bits/stdc++.h>
      |          ^~~~~~~~~~~~~~~
compilation terminated.