Submission #401245

#	Time	Username	Problem	Language	Result	Execution time	Memory
401245		galca	A Difficult(y) Choice (BOI21_books)	C++14	100 / 100	2 ms	1096 KiB

books

#include <iostream>
#include <vector>
#include <set>
using namespace std;

#include "books.h"

int findA(vector<long long>& books, long long A, int lower, int upper) {
	if (books[lower] == -1) {
		books[lower] = skim(lower + 1);
	}
	if (books[upper] == -1) {
		books[upper] = skim(upper + 1);
	}
	if (books[lower] > A) {
		return -1;
	}
	if (books[upper] <= A) {
		return upper;
	}

	if (upper - lower < 2) {
		return lower;
	}

	int half = (upper - lower + 1) / 2;
	books[lower + half] = skim(lower + half + 1);

	if (books[lower + half] <= A) return findA(books, A, lower + half, upper);
	else return findA(books, A, lower, lower + half);
}

void solve(int N, int K, long long A, int S) {
	if (K > N) {
		impossible();
		return;
	}
	vector<long long> books(N);

	for (int i = 0; i < N; i++) {
		books[i] = -1;
	}

	long long sumFirstK = 0;
	for (int i = 0; i < K; i++) {
		if (books[i] == -1) {
			books[i] = skim(i + 1);
		}
		sumFirstK += books[i];
	}

	if (sumFirstK > A * 2) {
		impossible();
	}
	else {
		vector<int> res;
		for (int i = 0; i < K; i++) {
			res.push_back(i + 1);
		}
		if (sumFirstK >= A) {
			answer(res);
		}
		else {
			// sumFirstK < A
			// find last element < A
			long long posA = findA(books, A, 0, N - 1);
			long long currentSum = sumFirstK;
			vector<int> attempt(res);
			// try to replace with largest values < A
			for (int i = 0; i < K; i++) {
				if (posA - i < 0) {
					break;
				}
				if (books[posA - i] == -1) {
					books[posA - i] = skim(posA - i + 1);
				}
				currentSum -= books[K - 1 - i];
				attempt[K - 1 - i] = posA - i + 1;
				currentSum += books[posA - i];
				if ((currentSum >= A) && (currentSum <= 2 * A)) {
					// check that no book appears twice
					set<int> validator;
					for (int j = 0; j < K; j++) {
						validator.insert(attempt[j]);
					}
					if (validator.size() == K) {
						answer(attempt);
						return;
					}
					break;
				}
			}
			// failed to build the sum with elements < A only
			// need to look at elements > A

			int j = 0;
			while ((j < K) && ((posA + 1 + j) < N)) {
				if (books[posA + j + 1] == -1) {
					books[posA + j + 1] = skim(posA + j + 2);
				}
				sumFirstK -= books[K - j - 1];
				res[K - j - 1] = posA + j + 2;
				sumFirstK += books[posA + j + 1];
				if (sumFirstK > A * 2) {
					impossible();
					return;
				}
				else {
					if (sumFirstK >= A) {
						set<int> validator;
						for (int l = 0; l < K; l++) {
							validator.insert(res[l]);
						}
						if (validator.size() == K) {
							answer(res);
						}
						else {
							impossible();
						}
						break;
					}
				}
				++j;
			}
			impossible();
		}
	}
	return;
}

Compilation message (stderr)

books.cpp: In function 'void solve(int, int, long long int, int)':
books.cpp:86:27: warning: comparison of integer expressions of different signedness: 'std::set<int>::size_type' {aka 'long unsigned int'} and 'int' [-Wsign-compare]
   86 |      if (validator.size() == K) {
      |          ~~~~~~~~~~~~~~~~~^~~~
books.cpp:114:28: warning: comparison of integer expressions of different signedness: 'std::set<int>::size_type' {aka 'long unsigned int'} and 'int' [-Wsign-compare]
  114 |       if (validator.size() == K) {
      |           ~~~~~~~~~~~~~~~~~^~~~

• 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