Submission #412939

#	Time	Username	Problem	Language	Result	Execution time	Memory
412939		amoo_safar	Sparklers (JOI17_sparklers)	C++17	50 / 100	2 ms	512 KiB

sparklers

// vaziat meshki-ghermeze !
#include <bits/stdc++.h>

#define pb push_back
#define F first
#define S second
#define all(x) x.begin(), x.end()
#define debug(x) cerr << #x << " : " << x << '\n'

using namespace std;

typedef long long ll;
typedef long double ld;
typedef string str;
typedef pair<ll, ll> pll;

const ll Mod = 1000000007LL;
const int N = 2e3 + 10;
const ll Inf = 2242545357980376863LL;
const ll Log = 30;

int n, k;
ll X[N];
ll psA[N], psB[N];

int dp[N][N];

bool Valid(vector<ll> psA, vector<ll> psB){
	int sa = psA.size(), sb = psB.size();
	int pa = 0, pb = 0;
	if(psA[sa - 1] + psB[sb - 1] < 0)
		return false;
	// cerr << "A :";
	// for(auto X : psA) cerr << ' ' << X;
	// cerr << '\n';
	// cerr << "B :";
	// for(auto X : psB) cerr << ' ' << X;
	// cerr << '\n';

	while((pa < sa - 1) || (pb < sb - 1)){
		ll nw = psA[pa] + psB[pb];
		if(nw < 0) return false;
		if(pa == sa - 1){
			pb ++;
			continue;
		}
		if(pb == sb - 1){
			pa ++;
			continue;
		}
		int des = pa;
		for(int nx = pa + 1; nx <= sa; nx ++){
			if(psA[nx] + psB[pb] < 0) break;
			if(psA[pa] <= psA[nx]){
				des = nx;
				break;
			}
		}
		if(des > pa){
			pa ++;
			continue;
		}
		des = pb;
		for(int nx = pb + 1; nx <= sb; nx ++){
			if(psA[pa] + psB[nx] < 0) break;
			if(psB[pb] <= psB[nx]){
				des = nx;
				break;
			}
		}
		if(des > pb){
			pb ++;
			continue;
		}
		////
		return false;
	}
	return true;
}

bool Check(ll T){
	if(T > 1000000000)
		return true;
	
	vector<ll> A = {T}, B = {};
	
	for(int i = k + 1; i <= n; i++){
		A.pb(X[i - 1] - X[i]);
		A.pb(T);
	}
	for(int i = k - 1; i >= 1; i--){
		B.pb(X[i] - X[i + 1]);
		B.pb(T);
	}
	psA[0] = 0;
	for(int i = 1; i <= (int) A.size(); i++)
		psA[i] = psA[i - 1] + A[i - 1];
	psB[0] = 0;
	for(int i = 1; i <= (int) B.size(); i++)
		psB[i] = psB[i - 1] + B[i - 1];

	// cerr << "#";
	// for(int i = 0; i <= (int) A.size(); i++)
	// 	cerr << ' ' << psA[i];
	// cerr << '\n';


	int idx = max_element(psA, psA + A.size() + 1) - psA;
	vector<ll> la, ra;
	for(int i = 0; i <= idx; i++) la.pb(psA[i]);
	for(int i = idx; i <= (int) A.size(); i++) ra.pb(psA[i]);
	// memset(dp, 0, sizeof dp);
	idx = max_element(psB, psB + B.size() + 1) - psB;
	vector<ll> lb, rb;
	for(int i = 0; i <= idx; i++) lb.pb(psB[i]);
	for(int i = idx; i <= (int) B.size(); i++) rb.pb(psB[i]);

	reverse(all(ra));
	reverse(all(rb));
	return Valid(la, lb) && Valid(ra, rb);
}

bool Check2(ll T){
	if(T > 1000000000)
		return true;
	vector<ll> A, B;
	A = {T};
	B = {};
	for(int i = k + 1; i <= n; i++){
		A.pb(X[i - 1] - X[i]);
		A.pb(T);
	}
	for(int i = k - 1; i >= 1; i--){
		B.pb(X[i] - X[i + 1]);
		B.pb(T);
	}
	psA[0] = 0;
	for(int i = 1; i <= (int) A.size(); i++)
		psA[i] = psA[i - 1] + A[i - 1];
	psB[0] = 0;
	for(int i = 1; i <= (int) B.size(); i++)
		psB[i] = psB[i - 1] + B[i - 1];
 
	memset(dp, 0, sizeof dp);
	int sa = A.size(), sb = B.size();
	dp[0][0] = 1;
	for(int i = 0; i <= sa; i++){
		for(int j = 0; j <= sb; j++){
			if(i + j == 0) continue;
			if(psA[i] + psB[j] < 0) continue;
			if(i)
				dp[i][j] |= dp[i - 1][j];
			if(j)
				dp[i][j] |= dp[i][j - 1];
		}
	}
	return dp[sa][sb];
}


int main(){
	ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
	ll T;
	cin >> n >> k >> T;
	for(int i = 1; i <= n; i++)
		cin >> X[i];

	int mid, L = -1, R = 1000000000;
	// int res = Check(2ll * T * 2);
	// debug(res);
	// exit(0);
	while(L + 1 < R){
		mid = (L + R) >> 1;
		// if(Check(2ll * T * mid) != Check2(2ll * T * mid)){
		// 	cerr << "!! " << mid << '\n';
		// 	if(Check2(2ll * T * mid))
		// 		assert(false);
		// }
		if(Check(2ll * T * mid))
			R = mid;
		else L = mid;
	}
	cout << R << '\n';
	return 0;
}

• Subtask 1: 30 / 30
• Subtask 2: 20 / 20
• Subtask 3: 0 / 50