Problem p03018 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
using namespace std;

#define rep(i, n) for (int i = 0; i < n; i++)
#define REP(i, s, n) for (int i = (s); i <= (n); i++)
#define repr(i, n) for (int i = n - 1; i >= 0; i--)
#define REPR(i, s, n) for (int i = (s); i >= (n); i--)
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define Eunique(v) v.erase(unique(all(v)), v.end())
#define Eback(s) s.erase(s.end() - 1, s.end())
#define rev(v) reverse(all(v))
#define minvec(v) *min_element(all(v))
#define maxvec(v) *max_element(all(v))
#define sumvec(v) accumulate(all(v), 0LL)
#define mapmin(v) v.rbegin()->first
#define mapmax(v) v.begin()->first
#define pb push_back
#define pf push_front
#define m_p make_pair
#define DOUBLE fixed << setprecision(15)
#define OK cerr << "OK\n"
#define OK1 cerr << "OK1\n"
#define OK2 cerr << "OK2\n"
#define SIZE(s) (int)s.size()
#define INF ((1LL << 62) - (1LL << 31))
#define zero(x, n) setw(x) << setfill('0') << n

typedef long long ll;

typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<long long> vll;
typedef vector<vll> vvll;
typedef vector<double> vd;
typedef vector<vd> vvd;
typedef vector<char> vc;
typedef vector<vc> vvc;
typedef vector<bool> vb;
typedef vector<vb> vvb;
typedef vector<string> vs;

typedef pair<ll, ll> pll;
typedef pair<int, int> pii;
typedef vector<pair<int, int>> vpii;
typedef vector<pair<ll, ll>> vpll;

const double pi = acos(-1.0);
const int mod = 1000000007;
const int mod2 = 998244353;

template <class A, class B>
ostream &operator<<(ostream &ost, const pair<A, B> &p) {
  ost << "{" << p.first << ", " << p.second << "} ";
  return ost;
}

template <class T> ostream &operator<<(ostream &ost, const vector<T> &v) {
  ost << "{";
  for (int i = 0; i < (int)v.size(); i++) {
    if (i)
      ost << " ";
    ost << v[i];
  }
  ost << "} \n";
  return ost;
}

template <class A, class B>
ostream &operator<<(ostream &ost, const map<A, B> &v) {
  ost << "{";
  for (auto p : v) {
    ost << "{" << p.first << ", " << p.second << "} ";
  }
  ost << "} ";
  return ost;
}

template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}

template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

void YES(bool b) { cout << ((b) ? "YES\n" : "NO\n"); }
void Yes(bool b) { cout << ((b) ? "Yes\n" : "No\n"); }
void yes(bool b) { cout << ((b) ? "yes\n" : "no\n"); }
void Yay(bool b) { cout << ((b) ? "Yay!\n" : ":(\n"); }

ll powmod(ll a, ll b) {
  ll c = 1;
  while (b > 0) {
    if (b & 1) {
      c = a * c % mod;
    }
    a = a * a % mod;
    b >>= 1;
  }
  return c;
}
ll gcd(ll x, ll y) { return __gcd(x, y); }
ll lcm(ll x, ll y) { return x / __gcd(x, y) * y; }

string replace_str(string &str, string from, string to) {
  const unsigned int pos = str.find(from);
  const int len = from.length();
  if (pos == string::npos || from.empty())
    return str;
  return str.replace(pos, len, to);
}

int main() {
  string s;
  cin >> s;
  while (s.find("BC") != string::npos)
    replace_str(s, "BC", "D");
  ll n = (ll)s.size();
  vs ss;
  string t = "";
  rep(i, n) {
    if (s[i] == 'A' || s[i] == 'D')
      t += s[i];
    else if (SIZE(t) != 0) {
      ss.pb(t);
      t = "";
    }
    if (i == n - 1 && SIZE(t) != 0)
      ss.pb(t);
  }
  ll ans = 0;
  for (auto &&e : ss) {
    ll cnt = 0, sum = 0;
    rep(i, (ll)e.size()) {
      if (e[i] == 'D') {
        sum += i - cnt;
        cnt++;
      }
    }
    ans += sum;
  }
  cout << ans << endl;
  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;

#define rep(i, n) for (int i = 0; i < n; i++)
#define REP(i, s, n) for (int i = (s); i <= (n); i++)
#define repr(i, n) for (int i = n - 1; i >= 0; i--)
#define REPR(i, s, n) for (int i = (s); i >= (n); i--)
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define Eunique(v) v.erase(unique(all(v)), v.end())
#define Eback(s) s.erase(s.end() - 1, s.end())
#define rev(v) reverse(all(v))
#define minvec(v) *min_element(all(v))
#define maxvec(v) *max_element(all(v))
#define sumvec(v) accumulate(all(v), 0LL)
#define mapmin(v) v.rbegin()->first
#define mapmax(v) v.begin()->first
#define pb push_back
#define pf push_front
#define m_p make_pair
#define DOUBLE fixed << setprecision(15)
#define OK cerr << "OK\n"
#define OK1 cerr << "OK1\n"
#define OK2 cerr << "OK2\n"
#define SIZE(s) (int)s.size()
#define INF ((1LL << 62) - (1LL << 31))
#define zero(x, n) setw(x) << setfill('0') << n

typedef long long ll;

typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<long long> vll;
typedef vector<vll> vvll;
typedef vector<double> vd;
typedef vector<vd> vvd;
typedef vector<char> vc;
typedef vector<vc> vvc;
typedef vector<bool> vb;
typedef vector<vb> vvb;
typedef vector<string> vs;

typedef pair<ll, ll> pll;
typedef pair<int, int> pii;
typedef vector<pair<int, int>> vpii;
typedef vector<pair<ll, ll>> vpll;

const double pi = acos(-1.0);
const int mod = 1000000007;
const int mod2 = 998244353;

template <class A, class B>
ostream &operator<<(ostream &ost, const pair<A, B> &p) {
  ost << "{" << p.first << ", " << p.second << "} ";
  return ost;
}

template <class T> ostream &operator<<(ostream &ost, const vector<T> &v) {
  ost << "{";
  for (int i = 0; i < (int)v.size(); i++) {
    if (i)
      ost << " ";
    ost << v[i];
  }
  ost << "} \n";
  return ost;
}

template <class A, class B>
ostream &operator<<(ostream &ost, const map<A, B> &v) {
  ost << "{";
  for (auto p : v) {
    ost << "{" << p.first << ", " << p.second << "} ";
  }
  ost << "} ";
  return ost;
}

template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}

template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

void YES(bool b) { cout << ((b) ? "YES\n" : "NO\n"); }
void Yes(bool b) { cout << ((b) ? "Yes\n" : "No\n"); }
void yes(bool b) { cout << ((b) ? "yes\n" : "no\n"); }
void Yay(bool b) { cout << ((b) ? "Yay!\n" : ":(\n"); }

ll powmod(ll a, ll b) {
  ll c = 1;
  while (b > 0) {
    if (b & 1) {
      c = a * c % mod;
    }
    a = a * a % mod;
    b >>= 1;
  }
  return c;
}
ll gcd(ll x, ll y) { return __gcd(x, y); }
ll lcm(ll x, ll y) { return x / __gcd(x, y) * y; }

string replace_str(string &str, string from, string to) {
  const unsigned int pos = str.find(from);
  const int len = from.length();
  if (pos == string::npos || from.empty())
    return str;
  return str.replace(pos, len, to);
}

int main() {
  string tmp, s = "";
  cin >> tmp;
  rep(i, SIZE(tmp) - 1) {
    if (tmp[i] == 'B' && tmp[i + 1] == 'C') {
      s += 'D';
      i++;
    } else
      s += tmp[i];
  }
  ll n = (ll)s.size();
  vs ss;
  string t = "";
  rep(i, n) {
    if (s[i] == 'A' || s[i] == 'D')
      t += s[i];
    else if (SIZE(t) != 0) {
      ss.pb(t);
      t = "";
    }
    if (i == n - 1 && SIZE(t) != 0)
      ss.pb(t);
  }
  ll ans = 0;
  for (auto &&e : ss) {
    ll cnt = 0, sum = 0;
    rep(i, (ll)e.size()) {
      if (e[i] == 'D') {
        sum += i - cnt;
        cnt++;
      }
    }
    ans += sum;
  }
  cout << ans << endl;
  return 0;
}