Problem p02692 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define F first
#define S second
#define pii pair<int, int>
#define eb emplace_back
#define all(v) v.begin(), v.end()
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep3(i, l, n) for (int i = l; i < (n); ++i)
#define sz(v) (int)v.size()
#define endl '\\n'
const int inf = 1000000007;
const ll INF = 1e18;
// int mod = 998244353;
int mod = 1000000007;
#define abs(x) (x >= 0 ? x : -(x))
#define lb(v, x) (int)(lower_bound(all(v), x) - v.begin())
#define ub(v, x) (int)(upper_bound(all(v), x) - v.begin())
template <typename T1, typename T2> inline bool chmin(T1 &a, T2 b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
template <typename T1, typename T2> inline bool chmax(T1 &a, T2 b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
ll gcd(ll a, ll b) {
  if (b == 0)
    return a;
  return gcd(b, a % b);
}
ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }
template <typename T, typename U> T pow_(T a, U b) {
  return b ? pow_(a * a, b / 2) * (b % 2 ? a : 1) : 1;
}
ll modpow(ll a, ll b, ll _mod) {
  return b ? modpow(a * a % _mod, b / 2, _mod) * (b % 2 ? a : 1) % _mod : 1;
}
template <class T, class U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
  os << p.F << " " << p.S;
  return os;
}
template <class T> ostream &operator<<(ostream &os, const vector<T> &vec) {
  rep(i, sz(vec)) {
    if (i)
      os << " ";
    os << vec[i];
  }
  return os;
}
template <typename T> inline istream &operator>>(istream &is, vector<T> &v) {
  rep(j, sz(v)) is >> v[j];
  return is;
}
template <class T, class T2> inline void add(T &a, T2 b) {
  a += b;
  if (a >= mod)
    a -= mod;
}

void solve();

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cout << fixed << setprecision(10);
  int T;
  T = 1;
  while (T--)
    solve();
}

// https://twitter.com/totori_kpr/status/1256941746866368513?s=20
void solve() {
  int n;
  cin >> n;
  vector<int> a(3);
  cin >> a;
  vector<string> s(n);
  cin >> s;
  vector<vector<int>> v(3);
  rep(i, sz(s)) rep(j, 2) v[s[i][j] - 'A'].eb(i);

  string ans;
  rep(i, n) {
    int x = s[i][0] - 'A', y = s[i][1] - 'A';
    if (a[x] > a[y])
      swap(x, y);
    // cout << x << " " << y << endl;
    if (a[x] < a[y]) {
      ans += 'A' + x;
      a[x]++;
      a[y]--;
    } else {
      if (a[x] == 0) {
        cout << "No" << endl;
        return;
      }
      int z = (x + 1) ^ (y + 1);
      --z;
      int it = ub(v[z], i);
      // cout << it << endl;
      if (it == sz(v[z])) {
        a[x]++;
        a[y]--;
        ans += 'A' + x;
      } else {
        // 次, x, y 以外が出る
        it = v[z][it];
        if (s[it][0] - 'A' == x || s[it][1] - 'A' == x) {
          a[x]++;
          a[y]--;
          ans += 'A' + x;
        } else { // y
          a[y]++;
          a[x]--;
          ans += 'A' + y;
        }
      }
    }
    // cout << a << endl;
  }
  cout << "Yes" << endl;
  rep(i, n) cout << ans[i] << endl;
}


Error: 0

Fixed submission:

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define F first
#define S second
#define pii pair<int, int>
#define eb emplace_back
#define all(v) v.begin(), v.end()
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep3(i, l, n) for (int i = l; i < (n); ++i)
#define sz(v) (int)v.size()
#define endl '\\n'
const int inf = 1000000007;
const ll INF = 1e18;
// int mod = 998244353;
int mod = 1000000007;
#define abs(x) (x >= 0 ? x : -(x))
#define lb(v, x) (int)(lower_bound(all(v), x) - v.begin())
#define ub(v, x) (int)(upper_bound(all(v), x) - v.begin())
template <typename T1, typename T2> inline bool chmin(T1 &a, T2 b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
template <typename T1, typename T2> inline bool chmax(T1 &a, T2 b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
ll gcd(ll a, ll b) {
  if (b == 0)
    return a;
  return gcd(b, a % b);
}
ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }
template <typename T, typename U> T pow_(T a, U b) {
  return b ? pow_(a * a, b / 2) * (b % 2 ? a : 1) : 1;
}
ll modpow(ll a, ll b, ll _mod) {
  return b ? modpow(a * a % _mod, b / 2, _mod) * (b % 2 ? a : 1) % _mod : 1;
}
template <class T, class U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
  os << p.F << " " << p.S;
  return os;
}
template <class T> ostream &operator<<(ostream &os, const vector<T> &vec) {
  rep(i, sz(vec)) {
    if (i)
      os << " ";
    os << vec[i];
  }
  return os;
}
template <typename T> inline istream &operator>>(istream &is, vector<T> &v) {
  rep(j, sz(v)) is >> v[j];
  return is;
}
template <class T, class T2> inline void add(T &a, T2 b) {
  a += b;
  if (a >= mod)
    a -= mod;
}

void solve();

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cout << fixed << setprecision(10);
  int T;
  T = 1;
  while (T--)
    solve();
}

// https://twitter.com/totori_kpr/status/1256941746866368513?s=20
void solve() {
  int n;
  cin >> n;
  vector<int> a(3);
  cin >> a;
  vector<string> s(n);
  cin >> s;
  vector<vector<int>> v(3);
  rep(i, sz(s)) {
    v[s[i][0] - 'A'].eb(i);
    v[s[i][1] - 'A'].eb(i);
  }
  // rep(i, 3) cout << v[i] << endl;

  string ans;
  rep(i, n) {
    int x = s[i][0] - 'A', y = s[i][1] - 'A';
    if (a[x] < a[y]) {
      ans += s[i][0];
      a[x]++;
      a[y]--;
    } else if (a[x] > a[y]) {
      ans += s[i][1];
      a[x]--;
      a[y]++;
    } else {
      if (a[x] == 0) {
        cout << "No" << endl;
        return;
      }
      int it = ub(v[x ^ y], i);
      if (it == sz(v[x ^ y])) {
        a[x]++;
        a[y]--;
        ans += 'A' + x;
      } else {
        // 次, x, y 以外が出る
        it = v[x ^ y][it];
        if (s[it][0] - 'A' == x || s[it][1] - 'A' == x) {
          a[x]++;
          a[y]--;
          ans += 'A' + x;
        } else { // y
          a[y]++;
          a[x]--;
          ans += 'A' + y;
        }
      }
      rep(j, 3) {
        if (a[j] < 0) {
          cout << "No" << endl;
          return;
        }
      }
    }
  }
  cout << "Yes" << endl;
  rep(i, n) cout << ans[i] << endl;
}