Problem p02648 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define all(x) (x).begin(), (x).end()
using namespace std;
using ll = long long;
using P = pair<int, int>;
template <class T> void chmin(T &a, const T &b) noexcept {
  if (b < a)
    a = b;
}
template <class T> void chmax(T &a, const T &b) noexcept {
  if (a < b)
    a = b;
}
void debug_out() { cout << "\\n"; }
template <class T, class... Args>
void debug_out(const T &x, const Args &...args) {
  cout << x << " ";
  debug_out(args...);
}
#ifdef _DEBUG
#define debug(...) debug_out(__VA_ARGS__)
#else
#define debug(...)
#endif

struct item_t {
  ll w, v;
  item_t(ll w, ll v) : w(w), v(v) {}
  item_t() : w(0), v(0) {}
  void operator+=(const item_t &r) {
    w += r.w;
    v += r.v;
  }
  bool operator<(const item_t &r) const { return w < r.w; }
};

vector<item_t> rekkyo(vector<item_t> item) {
  vector<item_t> a(1, item_t(0, 0));
  for (auto i : item) {
    vector<item_t> b = a, c;
    for (auto &e : b) {
      e += i;
    }
    std::merge(a.begin(), a.end(), b.begin(), b.end(), std::back_inserter(c));
    a = c;
  }
  return a;
}

int main() {
  std::cin.tie(nullptr);
  std::ios_base::sync_with_stdio(false);
  std::cout << std::fixed << std::setprecision(15);
  int n;
  cin >> n;
  vector<item_t> item(n + 1); // 1-indexed
  rep(i, n) cin >> item[i + 1].v >> item[i + 1].w;
  int q;
  cin >> q;
  while (q--) {
    int v, L;
    cin >> v >> L;
    vector<item_t> A;
    while (v > 0) {
      A.emplace_back(item[v]);
      v /= 2;
    }
    int m = A.size();
    auto a = rekkyo({A.begin(), A.begin() + m / 2});
    auto b = rekkyo({A.begin() + m / 2, A.end()});
    ll maxv = 0;
    for (auto &&x : b) { // x.v <- x.w以下で達成できる価値の最大値
      chmax(maxv, x.v);
      x.v = maxv;
    }
    reverse(all(a));
    ll ans = 0;
    int r = 0;
    for (auto &&x : a) {
      while (r + 1 < (int)b.size() && x.w + b[r + 1].w <= L) {
        r++;
      }
      if (x.w + b[r].w > L)
        continue;
      chmax(ans, x.v + b[r].v);
    }
    cout << ans << "\\n";
  }
  return 0;
}

Error: TLE

Fixed submission:

#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define all(x) (x).begin(), (x).end()
using namespace std;
using ll = long long;
using P = pair<int, int>;
template <class T> void chmin(T &a, const T &b) noexcept {
  if (b < a)
    a = b;
}
template <class T> void chmax(T &a, const T &b) noexcept {
  if (a < b)
    a = b;
}
void debug_out() { cout << "\\n"; }
template <class T, class... Args>
void debug_out(const T &x, const Args &...args) {
  cout << x << " ";
  debug_out(args...);
}
#ifdef _DEBUG
#define debug(...) debug_out(__VA_ARGS__)
#else
#define debug(...)
#endif

struct item_t {
  ll w, v;
  item_t(ll w, ll v) : w(w), v(v) {}
  item_t() : w(0), v(0) {}
  void operator+=(const item_t &r) {
    w += r.w;
    v += r.v;
  }
  bool operator<(const item_t &r) const { return w < r.w; }
};

vector<item_t> rekkyo(vector<item_t> item) {
  vector<item_t> a(1, item_t(0, 0));
  for (auto i : item) {
    vector<item_t> b = a, c;
    for (auto &e : b) {
      e += i;
    }
    std::merge(a.begin(), a.end(), b.begin(), b.end(), std::back_inserter(c));
    a = c;
  }
  return a;
}

int main() {
  std::cin.tie(nullptr);
  std::ios_base::sync_with_stdio(false);
  std::cout << std::fixed << std::setprecision(15);
  int n;
  cin >> n;
  vector<item_t> item(n + 1); // 1-indexed
  rep(i, n) cin >> item[i + 1].v >> item[i + 1].w;
  int q;
  cin >> q;
  while (q--) {
    int v, L;
    cin >> v >> L;
    vector<item_t> a;
    while (v > 0) {
      a.emplace_back(item[v]);
      v /= 2;
    }
    int m = a.size();
    auto b = rekkyo({a.begin(), a.begin() + m / 2});
    auto c = rekkyo({a.begin() + m / 2, a.end()});
    ll ans = 0;
    for (auto &&x : b) {
      if (x.w > L)
        continue;
      for (auto &&y : c) {
        if (x.w + y.w > L)
          break;
        chmax(ans, x.v + y.v);
      }
    }
    cout << ans << "\\n";
  }
  return 0;
}