Submission #956468

#	Time	Username	Problem	Language	Result	Execution time	Memory
956468		kilkuwu	A Difficult(y) Choice (BOI21_books)	C++17	100 / 100	1 ms	1444 KiB

books

#include <bits/stdc++.h>

#include "books.h"

using namespace std;
//
// --- Sample implementation for the task books ---
//
// To compile this program with the sample grader, place:
//     books.h books_sample.cpp sample_grader.cpp
// in a single folder and run:
//     g++ books_sample.cpp sample_grader.cpp
// in this folder.
//

void solve(int N, int K, long long A, int S) {
  // first K - 1 books
  // and first one >= A 
  // >= 2 * A -> impossible
  std::vector<long long> mem(N, -1);

  auto ask = [&](int i) {
    assert(0 <= i && i < N);
    if (mem[i] != -1) return mem[i];
    return mem[i] = skim(i + 1);
  };

  long long sum = 0;
  for (int i = 0; i < K; i++) {
    sum += ask(i);
  }

  if (sum > 2 * A) {
    impossible();
    return;
  }
  
  if (sum >= A) {
    std::vector<int> res(K);
    std::iota(res.begin(), res.end(), 1);
    answer(res);
    return;
  }

  // sum < A now
  int lb = K, rb = N;
  while (lb < rb) {
    int mid = (lb + rb) / 2;
    if (ask(mid) > A) {
      rb = mid;
    } else {
      lb = mid + 1;
    }
  }

  int id = rb;

  if (id < N) {
    auto ssum = sum + ask(id) - ask(K - 1);
    if (ssum >= A && ssum <= 2 * A) {
      std::vector<int> res;
      for (int i = 0; i < K - 1; i++) {
        res.emplace_back(i + 1);
      }
      res.emplace_back(id + 1);
      answer(res);
      return;
    }
    
  }

  std::vector<int> res_right;
  for (int i = id - 1; i >= std::max(K, id - K); i--) {
    res_right.emplace_back(i);
    ask(i);
  }

  // we know first sol is not working

  std::vector<int> res_left;
  for (int i = 0; i < K; i++) {
    res_left.push_back(i);
  }

  while (res_right.size()) {
    sum -= ask(res_left.front());
    res_left.erase(res_left.begin());
    sum += ask(res_right.back());
    res_left.emplace_back(res_right.back());
    res_right.pop_back();

    if (sum >= A) {
      // we good 
      for (int& x : res_left) x++;
      answer(res_left);
      return;
    }
  }

  impossible();
}

• Subtask 1: 5 / 5
• Subtask 2: 15 / 15
• Subtask 3: 10 / 10
• Subtask 4: 15 / 15
• Subtask 5: 15 / 15
• Subtask 6: 20 / 20
• Subtask 7: 20 / 20