Problem p02692 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <cmath>
#include <complex>
#include <cstdint>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <regex>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;
using ll = long long;
using ull = unsigned long long;

namespace utils {
#define ALL(x) begin(x), end(x)
#define RALL(x) rbegin(x), rend(x)
template <class T, class Compare>
using p_queue = priority_queue<T, vector<T>, Compare>;
template <class T> using min_queue = p_queue<T, greater<T>>;
template <class T> using max_queue = p_queue<T, less<T>>;

template <class T> inline bool UPMIN(T &X, const T &A) {
  if (X > A) {
    X = A;
    return true;
  }
  return false;
}
template <class T> inline bool UPMAX(T &X, const T &A) {
  if (X < A) {
    X = A;
    return true;
  }
  return false;
}

template <class T> vector<T> VEC(int n, T t) { return vector<T>(n, t); }
template <class... Ts> auto VEC(int n, Ts... ts) {
  return vector<decltype(VEC(ts...))>(n, VEC(ts...));
}

template <class S, class T> istream &operator>>(istream &is, tuple<S, T> &t) {
  return is >> get<0>(t) >> get<1>(t);
}

template <class S, class T, class U>
istream &operator>>(istream &is, tuple<S, T, U> &t) {
  return is >> get<0>(t) >> get<1>(t) >> get<2>(t);
}

template <class S, class T>
ostream &operator<<(ostream &os, const tuple<S, T> &t) {
  return os << get<0>(t) << ' ' << get<1>(t);
}

template <class S, class T, class U>
ostream &operator<<(ostream &os, const tuple<S, T, U> &t) {
  return os << get<0>(t) << ' ' << get<1>(t) << ' ' << get<2>(t);
}

template <class T> istream &operator>>(istream &is, vector<T> &v) {
  for (auto &&x : v) {
    is >> x;
  }
  return is;
}

template <class T> ostream &operator<<(ostream &os, const vector<T> &v) {
  auto p = v.begin();
  assert(p != v.end());
  os << *p++;
  while (p != v.end()) {
    os << ' ' << *p++;
  }
  return os;
}

template <class T>
ostream &operator<<(ostream &os, const vector<vector<T>> &v) {
  auto p = v.begin();
  assert(p != v.end());
  os << *p++;
  while (p != v.end()) {
    os << '\n' << *p++;
  }
  return os;
}

template <class... Ts>
ostream &operator<<(ostream &os, const vector<tuple<Ts...>> &v) {
  auto p = v.begin();
  assert(p != v.end());
  os << *p++;
  while (p != v.end()) {
    os << '\n' << *p++;
  }
  return os;
}

constexpr long long INFLL = 1'000'000'000'000'000'000ll;
constexpr int INF = 1'000'000'000;
constexpr double PI = 3.14'159'265'358'973;
constexpr double EPS = 1e-10;
} // namespace utils
using namespace utils;

class solver {
  istream &is;
  ostream &os;

public:
  solver(istream &I, ostream &O) : is(I), os(O) {}

  int N;
  vector<int> ABC;
  vector<pair<int, int>> S;
  bool input() {
    ABC.resize(3);
    is >> N >> ABC;
    S.resize(N);
    for (int i = 0; i < N; ++i) {
      char s1, s2;
      is >> s1 >> s2;
      S[i] = {s1 - 'A', s2 - 'A'};
    } // end i
    return !!is;
  }

  string greed(int k) {
    stringstream ans;
    for (int i = k; i < N; ++i) {
      int x, y;
      tie(x, y) = S[i];
      if (ABC[x] < ABC[y]) {
        ans << char(x + 'A') << '\n';
        ABC[x]++;
        ABC[y]--;
      } else if (ABC[x] == 0) {
        return "No\n";
      } else {
        ans << char(y + 'A') << '\n';
        ABC[x]--;
        ABC[y]++;
      }
    } // end i
    cout << "Yes\n";
    return ans.str();
  }

  string dfs(int i) {
    if (ABC[0] < 0 or ABC[1] < 0 or ABC[2] < 0) {
      assert(false);
    }
    if (i == N) {
      return "";
    }
    int x, y;
    tie(x, y) = S[i];
    if (ABC[x] > 0) {
      ABC[x]--;
      ABC[y]++;
      string f = dfs(i + 1);
      if (f[0] != '-') {
        return f + char('A' + y);
      }
      ABC[x]++;
      ABC[y]--;
    }
    if (ABC[y] > 0) {
      ABC[y]--;
      ABC[x]++;
      string f = dfs(i + 1);
      if (f[0] != '-') {
        return f + char('A' + x);
      }
      ABC[x]++;
      ABC[y]--;
    }

    return "-";
  }

  void run();
};

int main(int argc, char *argv[]) {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  cout << setprecision(16) << scientific;
#ifdef XELMH
  string test_cases = "test_F.txt";
  cerr << test_cases << " -->" << endl;
  auto fs = fstream(test_cases, fstream::in);
  int loop = 0;
  while (fs) {
    loop++;
    cout << '#' << loop << "#------\n";
    solver(fs, cout).run();
  }
  if (loop <= 1) {
    cout << "===" << endl;
    while (cin)
      solver(cin, cout).run();
  }
#else
  solver(cin, cout).run();
#endif
  return 0;
}

void solver::run() {
  if (!input())
    return;
  ll sum = min(ABC[0], 3) + min(ABC[1], 3) + ABC[2];
  if (sum > 2) {
    os << greed(0);
    return;
  }
  //    assert(false);
  //    cout << "No\n";

  string ans = dfs(0);
  if (ans.empty() or ans[0] == '-') {
    os << "No\n";
  } else {
    os << "Yes\n";
    for (int k = ans.size() - 1; k >= 0; --k) {
      cout << ans[k] << endl;

    } // end k
  }
}


Fixed submission:
#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <cmath>
#include <complex>
#include <cstdint>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <regex>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;
using ll = long long;
using ull = unsigned long long;

namespace utils {
#define ALL(x) begin(x), end(x)
#define RALL(x) rbegin(x), rend(x)
template <class T, class Compare>
using p_queue = priority_queue<T, vector<T>, Compare>;
template <class T> using min_queue = p_queue<T, greater<T>>;
template <class T> using max_queue = p_queue<T, less<T>>;

template <class T> inline bool UPMIN(T &X, const T &A) {
  if (X > A) {
    X = A;
    return true;
  }
  return false;
}
template <class T> inline bool UPMAX(T &X, const T &A) {
  if (X < A) {
    X = A;
    return true;
  }
  return false;
}

template <class T> vector<T> VEC(int n, T t) { return vector<T>(n, t); }
template <class... Ts> auto VEC(int n, Ts... ts) {
  return vector<decltype(VEC(ts...))>(n, VEC(ts...));
}

template <class S, class T> istream &operator>>(istream &is, tuple<S, T> &t) {
  return is >> get<0>(t) >> get<1>(t);
}

template <class S, class T, class U>
istream &operator>>(istream &is, tuple<S, T, U> &t) {
  return is >> get<0>(t) >> get<1>(t) >> get<2>(t);
}

template <class S, class T>
ostream &operator<<(ostream &os, const tuple<S, T> &t) {
  return os << get<0>(t) << ' ' << get<1>(t);
}

template <class S, class T, class U>
ostream &operator<<(ostream &os, const tuple<S, T, U> &t) {
  return os << get<0>(t) << ' ' << get<1>(t) << ' ' << get<2>(t);
}

template <class T> istream &operator>>(istream &is, vector<T> &v) {
  for (auto &&x : v) {
    is >> x;
  }
  return is;
}

template <class T> ostream &operator<<(ostream &os, const vector<T> &v) {
  auto p = v.begin();
  assert(p != v.end());
  os << *p++;
  while (p != v.end()) {
    os << ' ' << *p++;
  }
  return os;
}

template <class T>
ostream &operator<<(ostream &os, const vector<vector<T>> &v) {
  auto p = v.begin();
  assert(p != v.end());
  os << *p++;
  while (p != v.end()) {
    os << '\n' << *p++;
  }
  return os;
}

template <class... Ts>
ostream &operator<<(ostream &os, const vector<tuple<Ts...>> &v) {
  auto p = v.begin();
  assert(p != v.end());
  os << *p++;
  while (p != v.end()) {
    os << '\n' << *p++;
  }
  return os;
}

constexpr long long INFLL = 1'000'000'000'000'000'000ll;
constexpr int INF = 1'000'000'000;
constexpr double PI = 3.14'159'265'358'973;
constexpr double EPS = 1e-10;
} // namespace utils
using namespace utils;

class solver {
  istream &is;
  ostream &os;

public:
  solver(istream &I, ostream &O) : is(I), os(O) {}

  int N;
  vector<int> ABC;
  vector<pair<int, int>> S;
  bool input() {
    ABC.resize(3);
    is >> N >> ABC;
    S.resize(N);
    for (int i = 0; i < N; ++i) {
      char s1, s2;
      is >> s1 >> s2;
      S[i] = {s1 - 'A', s2 - 'A'};
    } // end i
    return !!is;
  }

  string greed(int k) {
    stringstream ans;
    for (int i = k; i < N; ++i) {
      int x, y;
      tie(x, y) = S[i];
      if (ABC[x] < ABC[y]) {
        ans << char(x + 'A') << '\n';
        ABC[x]++;
        ABC[y]--;
      } else if (ABC[x] == 0) {
        return "No\n";
      } else {
        ans << char(y + 'A') << '\n';
        ABC[x]--;
        ABC[y]++;
      }
    } // end i
    cout << "Yes\n";
    return ans.str();
  }

  string dfs(int i) {
    if (ABC[0] < 0 or ABC[1] < 0 or ABC[2] < 0) {
      return "-";
    }
    if (i == N) {
      return "";
    }
    int x, y;
    tie(x, y) = S[i];
    if (ABC[x] > 0) {
      ABC[x]--;
      ABC[y]++;
      string f = dfs(i + 1);
      if (f[0] != '-') {
        return f + char('A' + y);
      }
      ABC[x]++;
      ABC[y]--;
    }
    if (ABC[y] > 0) {
      ABC[y]--;
      ABC[x]++;
      string f = dfs(i + 1);
      if (f[0] != '-') {
        return f + char('A' + x);
      }
      ABC[x]++;
      ABC[y]--;
    }

    return "-";
  }

  void run();
};

int main(int argc, char *argv[]) {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  cout << setprecision(16) << scientific;
#ifdef XELMH
  string test_cases = "test_F.txt";
  cerr << test_cases << " -->" << endl;
  auto fs = fstream(test_cases, fstream::in);
  int loop = 0;
  while (fs) {
    loop++;
    cout << '#' << loop << "#------\n";
    solver(fs, cout).run();
  }
  if (loop <= 1) {
    cout << "===" << endl;
    while (cin)
      solver(cin, cout).run();
  }
#else
  solver(cin, cout).run();
#endif
  return 0;
}

void solver::run() {
  if (!input())
    return;
  ll sum = min(ABC[0], 3) + min(ABC[1], 3) + ABC[2];
  if (sum > 2) {
    os << greed(0);
    return;
  }
  //    assert(false);
  //    cout << "No\n";

  string ans = dfs(0);
  if (ans.empty() or ans[0] == '-') {
    os << "No\n";
  } else {
    os << "Yes\n";
    for (int k = ans.size() - 1; k >= 0; --k) {
      cout << ans[k] << endl;

    } // end k
  }
}