Language: C++

#pragma region kyomukyomupurin

/**
 *    author  : 𝒌𝒚𝒐𝒎𝒖𝒌𝒚𝒐𝒎𝒖𝒑𝒖𝒓𝒊𝒏
 *    created : 2020-06-27 23:18:57
 **/

#include <algorithm>
#include <bitset>
#include <cassert>
#include <cctype>
#include <chrono>
#include <cmath>
#include <complex>
#include <deque>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <utility>
#include <vector>

using namespace std;

using int64 = long long;

template<class T>
inline void eraque(std::vector<T>& vec) {
  vec.erase(std::unique(vec.begin(), vec.end()), vec.end());
  return;
}

template<class T>
inline int lower_position(const std::vector<T>& vec, T value) {
  return static_cast<int>(std::distance(vec.begin(), std::lower_bound(vec.begin(), vec.end(), value)));
}

template<class T>
inline int upper_position(const std::vector<T>& vec, T value) {
  return static_cast<int>(std::distance(vec.begin(), std::upper_bound(vec.begin(), vec.end(), value)));
}

template <class T>
using binary_heap = std::priority_queue<T, std::vector<T>, std::greater<T>>;

template <class T, class U>
std::ostream& operator<<(std::ostream& os, const std::pair<T, U>& p) {
  return os << '(' << p.first << ", " << p.second << ')';
}

template <class Tuple, std::size_t... Is>
void tuple_out(std::ostream& os, const Tuple& tp, std::index_sequence<Is...>) {
  ((os << (Is ? ", " : "(") << std::get<Is>(tp)), ...) << ")";
}

template <class... Args>
std::ostream& operator<<(std::ostream& os, const std::tuple<Args...>& tp) {
  tuple_out(os, tp, std::index_sequence_for<Args...>{});
  return os;
}

template <class T>
std::ostream& operator<<(std::ostream& os, const std::vector<T>& vec) {
  int n = 0;
  for (auto e : vec) os << (n++ ? ", " : "{") << e;
  return os << (n ? "}" : "{}");
}

template <class T, class Compare>
std::ostream& operator<<(std::ostream& os, const std::set<T, Compare>& st) {
  int n = 0;
  for (auto e : st) os << (n++ ? ", " : "{") << e;
  return os << (n ? "}" : "{}");
}

template <class T, class U, class Compare>
std::ostream& operator<<(std::ostream& os, const std::map<T, U, Compare>& mp) {
  int n = 0;
  for (auto e : mp) os << (n++ ? ", " : "{") << e;
  return os << (n ? "}" : "{}");
}

template <class T>
std::istream& operator>>(std::istream& is, std::vector<T>& vec) {
  for (T& e : vec) is >> e;
  return is;
}

template <class T, class U>
std::istream& operator>>(std::istream& is, std::pair<T, U>& p) {
  return is >> p.first >> p.second;
}

template <class Tuple, std::size_t... Is>
void tuple_in(std::istream& is, Tuple& tp, std::index_sequence<Is...>) {
  ((is >> std::get<Is>(tp)), ...);
}

template <class... Args>
std::istream& operator>>(std::istream& is, std::tuple<Args...>& tp) {
  tuple_in(is, tp, std::index_sequence_for<Args...>{});
  return is;
}

#define all(_) begin(_), end(_)
#define rall(_) rbegin(_), rend(_)

#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]: ", debug_out(__VA_ARGS__)
#else
#define debug(...)
#endif

void debug_out() { std::cerr << '\n'; }

template <class Head, class... Tail>
void debug_out(Head&& head, Tail&&... tail) {
  std::cerr << head;
  if (sizeof...(Tail) != 0) std::cerr << ", ";
  debug_out(std::forward<Tail>(tail)...);
}

#pragma endregion kyomukyomupurin

class Scanner {
  static constexpr int buf_size = (1 << 18);
  static constexpr int integer_size = 20;
  char buf[buf_size] = {};
  char *beg = buf, *end = buf;

 public:
  Scanner() {}

  ~Scanner() {}

  template<class T>
  inline Scanner& operator>>(T& val) {
    read(val);
    return *this;
  }

 private:
  inline void flush() {
    size_t len = end - beg;
    memmove(buf, beg, len);
    char *tmp = buf + len;
    end = tmp + fread(tmp, 1, buf_size - len, stdin);
    *end = 0;
    beg = buf;
  }

  inline void skip_space() {
    while (true) {
      if (beg == end) flush();
      while(std::isspace(*beg)) ++beg;
      if (__builtin_expect(beg != end, 1)) return;
    }
  }

  template <class T, std::enable_if_t<std::is_same<T, int>::value, int> = 0>
  inline void read(T& num) {
    skip_space();
    if (beg + integer_size >= end) flush();
    bool neg = false;
    num = 0;
    while (!std::isdigit(*beg) && *beg != '-') ++beg;
    if (*beg == '-') neg = true, ++beg;
    while (std::isdigit(*beg)) num = num * 10 + (*beg - '0'), ++beg;
    if (neg) num = -num;
  }

  template <class T, std::enable_if_t<std::is_same<T, int64>::value, int> = 0>
  inline void read(T& num) {
    skip_space();
    if (beg + integer_size >= end, 0) flush();
    bool neg = false;
    num = 0;
    while (!std::isdigit(*beg) && *beg != '-') ++beg;
    if (*beg == '-') neg = true, ++beg;
    while (std::isdigit(*beg)) num = num * 10 + (*beg - '0'), ++beg;
    if (neg) num = -num;
  }

  template <class T,
            std::enable_if_t<std::is_same<T, std::string>::value, int> = 0>
  inline void read(T& str) {
    skip_space();
    if (beg + str.size() >= end, 0) flush();
    auto it = beg;
    while (!std::isspace(*beg)) ++beg;
    str = std::string(it, beg);
  }

  template <class T, std::enable_if_t<std::is_same<T, char>::value, int> = 0>
  inline void read(T& c) {
    skip_space();
    if (beg + 1 >= end, 0) flush();
    c = *beg, ++beg;
  }

  template <class T>
  inline void read(std::vector<T>& vec) {
    for (T& e : vec) read(e);
  }

  template <class T, class U>
  inline void read(std::pair<T, U>& p) {
    read(p.first, p.second);
  }

  template <class Tuple, std::size_t... Is>
  inline void tuple_scan(Tuple& tp, std::index_sequence<Is...>) {
    (read(std::get<Is>(tp)), ...);
  }

  template <class... Args>
  inline void read(std::tuple<Args...>& tp) {
    tuple_scan(tp, std::index_sequence_for<Args...>{});
  }

  inline void read() {}

  template <class Head, class... Tail>
  inline void read(Head&& head, Tail&&... tail) {
    read(head);
    read(std::forward<Tail>(tail)...);
  }
};

Scanner sc;

template <class _Tp>
class CumulativeSum {
 public:
  CumulativeSum(const std::vector<_Tp>& vec) : vec_(vec) { build(); }

  // return sum of [l, r]
  _Tp get(int l, int r) { return sum_[r + 1] - sum_[l]; }

  // return the first k where sum of [0, k] >= value
  // use only when all element in vec >= 0
  int lower_bound(_Tp value) {
    return std::distance(sum_.begin() + 1,
                         std::lower_bound(sum_.begin() + 1, sum_.end(), value));
  }

  // return the first k where sum of [0, k] > value
  // use only when all element in vec >= 0
  int upper_bound(_Tp value) {
    return std::distance(sum_.begin() + 1,
                         std::upper_bound(sum_.begin() + 1, sum_.end(), value));
  }

 private:
  std::vector<_Tp> vec_;
  std::vector<_Tp> sum_;

  void build() {
    sum_.assign(vec_.size() + 1, static_cast<_Tp>(0));
    for (size_t i = 0; i < vec_.size(); ++i) {
      sum_[i + 1] = sum_[i] + vec_[i];
    }
  }
};


int main() {
  //ios_base::sync_with_stdio(false);
  //cin.tie(nullptr);

  int n, m, k; sc >> n >> m >> k;
  vector<int64> a(n), b(m); sc >> a >> b;
  CumulativeSum<int64> csa(a);
  CumulativeSum<int64> csb(b);
  
  int high = n + m + 1, low = 0;

  while (high - low > 1) {
    int mid = (high + low) >> 1;
    int64 need = 1e18;
    int can = 0;

    if (n >= mid) need = min(need, csa.get(0, mid - 1));
    if (m >= mid) need = min(need, csb.get(0, mid - 1));

    for (int i = 0; i < n; ++i) {
      if (mid - i - 2 < 0 || mid - i - 2 >= m) continue;
      need = min(need, csa.get(0, i) + csb.get(0, mid - i - 2));
    }

    if (need > k) {
      high = mid;
    } else {
      low = mid;
    }
  }

  cout << low << endl;

  return 0;
}


Compiler output:
a.cc: In member function 'void Scanner::flush()':
a.cc:151:5: error: 'memmove' was not declared in this scope
  151 |     memmove(buf, beg, len);
      |     ^~~~~~~
a.cc:27:1: note: 'memmove' is defined in header '<cstring>'; this is probably fixable by adding '#include <cstring>'
   26 | #include <utility>
  +++ |+#include <cstring>
   27 | #include <vector>