Submission #724730

#	Time	Username	Problem	Language	Result	Execution time	Memory
724730		406	Sparklers (JOI17_sparklers)	C++17	100 / 100	70 ms	4424 KiB

sparklers

#include "bits/stdc++.h"
#define int long long
#define dq deque<int>
using namespace std;
const long long INF = 1ll << 35;
const int N = 1e5 + 5;
int n, k, t, x[N];
dq L, R;

void ps(dq &v) {
	v.push_front(0);
	for (int i = 1; i < v.size(); i++) v[i] += v[i - 1];
}

array<int, 3> find(const dq &v) {
	int mn = v[0];
	for (int i = 1; i < v.size(); i++) {
		int u = v[i];
		mn = min(mn, u);
		if (u >= v[0]) return {u, mn, 1};
	}
	return {0, 0, 0};
}

bool solve(array<dq, 2> v, int d = 0) {
	if (v[0][0] + v[1][0] < 0 || v[1].back() + v[0].back() < 0) return false;

	assert(d <= 1);

	array<int, 3> A[2];
	A[0] = find(v[0]);
	A[1] = find(v[1]);

	while (v[0].size() > 1 && v[1].size() > 1) {
		//cout << v[0].size() << ' ' << v[1].size() << endl;
		bool flag = false;

		for (int k = 0; k < 2; k++) if (A[k][2]) {
			if (v[k ^ 1][0] + A[k][1] >= 0) {
				v[k].pop_front();
				while (v[k][0] != A[k][0]) v[k].pop_front();
				A[k] = find(v[k]);
				flag = true;
			}
		}

		if (flag) continue;
		else if (A[0][2] && A[1][2]) return false;

		if (!A[0][2] && !A[1][2]) {
			for (int k = 0; k < 2; k++) reverse(v[k].begin(), v[k].end());
			return solve(v, d + 1);
		}
		else return false;
	}
	for (int k = 0; k < 2; k++) if (v[k].size() > 1) {
		for (auto u: v[k]) if (u + v[1 ^ k][0] < 0) return false;
	}
	return true;
}

bool check(int O) {
	int s = O * 2 * t;
	dq l = L, r = R;
	for (auto &u: l) u = s - u;
	for (auto &u: r) u = s - u;
	ps(l), ps(r);

	/*
	for (auto u: l) cout << u << ' ';
	cout << endl;
	for (auto u: r) cout << u << ' ';
	cout << endl;
	*/

	return solve(array<dq, 2>{l, r});
}

void rand_test();

signed main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
	cin >> n >> k >> t;
	k--;

	for (int i = 0; i < n; i++) cin >> x[i];
	for (int i = 0; i < k; i++)
		L.push_back(x[i + 1] - x[i]);	
	reverse(L.begin(), L.end());
	for (int i = k + 1; i < n; i++) 
		R.push_back(x[i] - x[i - 1]);

	int l = -1, r = INF;
	while (r - l > 1) {
		int m = l + r >> 1;
		if (check(m)) r = m;
		else l = m;
	}
	cout << r << '\n';
	return 0;
}

void rand_test() {
	for (int i = 0; i < 20; i++) L.push_back(rand() % 10);
	for (int i = 0; i < 20; i++) R.push_back(rand() % 10);
	for (auto u: L) cout << u << ' ';
	cout << endl;
	for (auto u: R) cout << u << ' ';
	cout << endl;
	solve(array<dq, 2>{L, R});
}

Compilation message (stderr)

sparklers.cpp: In function 'void ps(std::deque<long long int>&)':
sparklers.cpp:12:20: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::deque<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   12 |  for (int i = 1; i < v.size(); i++) v[i] += v[i - 1];
      |                  ~~^~~~~~~~~~
sparklers.cpp: In function 'std::array<long long int, 3> find(const std::deque<long long int>&)':
sparklers.cpp:17:20: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::deque<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   17 |  for (int i = 1; i < v.size(); i++) {
      |                  ~~^~~~~~~~~~
sparklers.cpp: In function 'int main()':
sparklers.cpp:96:13: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
   96 |   int m = l + r >> 1;
      |           ~~^~~

• Subtask 1: 30 / 30
• Subtask 2: 20 / 20
• Subtask 3: 50 / 50