Submission #1226505

#	Time	Username	Problem	Language	Result	Execution time	Memory
1226505		_rain_	Sparklers (JOI17_sparklers)	C++20	100 / 100	12 ms	1628 KiB

sparklers

#include<bits/stdc++.h>
using namespace std;
typedef long long LL;

const int N=(int)1e6;
const long double eps=1e-17;
	int x[N+2];
	int n,k;
LL X[N+2];
LL t;

	bool maximize(LL &x,LL y){
		if (x<=y) return x=y,true;
		return false;
	}
	bool minimize(LL &x,LL y){
		if (x>=y) return x=y,true;
		return false;
	}


bool possible(LL s){
	if (s==0){
		for(int i=2;i<=n;++i) if (x[i]!=x[i-1]) return false;
		return true;
	}
	for(int i=1;i<=n;++i) X[i]=x[i]-s*t*2*i;
	
	int l=k,r=k;
	int gl=k,gr=k;
	bool nxt=true;
	while (nxt){
		
		nxt=false;
		LL mx;
		int tmp_l=l,best_l=l;
		mx=X[l];
		while (tmp_l>=1 && X[tmp_l]>=X[r]){
			if (maximize(mx,X[tmp_l])) best_l=tmp_l;
			--tmp_l;
		}
		if (l!=best_l) {
			l=best_l;
			gl=l;
			nxt=true;
		}
		int tmp_r=r,best_r=r;
		mx=X[r];
		while (tmp_r<=n && X[l]>=X[tmp_r]){
			if (minimize(mx,X[tmp_r])) best_r=tmp_r;
			++tmp_r;
		}
		if (best_r!=r){
			r=best_r;
			gr=r;
			nxt=true;
		}
	}
	
	l=1,r=n;
	nxt=true;
	while (nxt){
		nxt=false;
		LL mx;
		int tmp_l=l,best_l=l;
		mx=X[l];
		while (tmp_l<=gl && X[tmp_l]>=X[r]){
			if (maximize(mx,X[tmp_l])) best_l=tmp_l;
			++tmp_l;
		}
		if (l!=best_l) {
			l=best_l;
			nxt=true;
		}
		int tmp_r=r,best_r=r;
		mx=X[r];
		while (tmp_r>=gr && X[l]>=X[tmp_r]){
			if (minimize(mx,X[tmp_r])) best_r=tmp_r;
			--tmp_r;
		}
		if (best_r!=r){
			r=best_r;
			nxt=true;
		}
	}
	return l==gl && r==gr;
	return true;
}

int main(){
	ios::sync_with_stdio(false);
	cin.tie(0) ; cout.tie(0);
	#define task "main"
	if (fopen(task".inp","r")){
		freopen(task".inp","r",stdin);
		freopen(task".out","w",stdout);
	}
	
	cin>>n>>k>>t;
	for(int i=1;i<=n;++i) cin>>x[i];
	int low=0,high=*max_element(x+1,x+n+1),ans=-1;
	while (low<=high){
		int mid=(low+high)/2;
		if (possible(mid)){
			ans=mid;
			high=mid-1;
		}
		else low=mid+1;
	}
	cout<<ans;
	return 0;
}

Compilation message (stderr)

sparklers.cpp: In function 'int main()':
sparklers.cpp:95:24: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   95 |                 freopen(task".inp","r",stdin);
      |                 ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
sparklers.cpp:96:24: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   96 |                 freopen(task".out","w",stdout);
      |                 ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~

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