Submission #1104942

#	Time	Username	Problem	Language	Result	Execution time	Memory
1104942		alexander707070	Ancient Books (IOI17_books)	C++14	50 / 100	123 ms	28744 KiB

books

#include<bits/stdc++.h>
#define MAXN 1000007
using namespace std;

int n,s,p[MAXN],fr,last,mins,maxs,pref[MAXN],curr;
bool li[MAXN];
long long ans;

int k,cycle[MAXN];
pair<int,int> where[MAXN];

void dfs(int x){
	li[x]=true;
	cycle[x]=k;

	ans+=abs(x-p[x]);
	mins=min(mins,x);
	maxs=max(maxs,x);

	if(!li[p[x]])dfs(p[x]);
}

long long minimum_walk(vector<int> P, int S){
	n=int(P.size()); s=S+1;

	for(int i=1;i<=n;i++){
		p[i]=P[i-1]+1;
		li[i]=false; pref[i]=0;
	}
	last=0; fr=n+1; k=0; ans=0;

	for(int i=1;i<=n;i++){
		if(!li[i]){
			if(p[i]!=i)last=i;
			dfs(i);
		}
	}

	for(int i=1;i<=n;i++)li[i]=false;

	for(int i=n;i>=1;i--){
		if(!li[i]){
			k++;
			if(p[i]!=i)fr=i;

			mins=n; maxs=1;
			dfs(i);

			where[k]={mins,maxs};
			pref[mins]++; pref[maxs]--;
		}
	}
	ans/=2;

	for(int i=1;i<=n-1;i++){
		curr+=pref[i];
		if(i<s)continue;

		if(curr==0 and last>i)ans+=2;
	}

	curr=0;
	for(int i=n;i>=2;i--){
		curr+=pref[i];
		if(i>s)continue;

		if(curr==0 and fr<i)ans+=2;
	}

	/// more steps inside initial cycle

	vector<int> l,r;

	int pt=s,from=s,to=s,ll=s,rr=s;

	while(true){
		if(ll>=from){
			from=min(from,where[cycle[ll]].first);
			to=max(to,where[cycle[ll]].second);
			ll--;
		}

		if(rr<=to){
			from=min(from,where[cycle[rr]].first);
			to=max(to,where[cycle[rr]].second);
			rr++;
		}

		if(ll<from and rr>to)break;
	}

	pt=to;
	
	while(pt<=n){
		int t=0;
		
		pt=where[cycle[pt]].second+1;
		t++;

		while(pt<=n and where[cycle[pt]].first>=s){
			to=max(to,where[cycle[pt]].second);

			if(pt==to){
				pt++; t++;
			}else{
				pt++;
			}
		}

		if(pt<=n)r.push_back(t);
	}

	pt=from;

	while(pt>1){
		int t=0;
		
		pt=where[cycle[pt]].first-1;
		t++;

		while(pt>=1 and where[cycle[pt]].second<=s){
			from=min(from,where[cycle[pt]].first);
			
			if(pt==from){
				pt--; t++;
			}else{
				pt--;
			}
		}

		if(pt>=1)l.push_back(t);
	}

	for(int i=0;i<l.size();i++){
		ans+=2*min(l[i],r[i]);
	}
	
	return ans;
}

/*int main(){

	vector<int> perm;
	for(int i=0;i<20;i++){
		perm.push_back(i);
	}

	while(true){
		random_shuffle(perm.begin(),perm.end());
		for(int i=0;i<20;i++){
			cout<<perm[i]<<" ";
		}
		cout<<"\n";

		int z=rand()%20;

		cout<<z<<"\n";
		minimum_walk(perm,z);
	}

	return 0;
}*/

Compilation message (stderr)

books.cpp: In function 'long long int minimum_walk(std::vector<int>, int)':
books.cpp:134:15: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  134 |  for(int i=0;i<l.size();i++){
      |              ~^~~~~~~~~

• Subtask 1: 12 / 12
• Subtask 2: 10 / 10
• Subtask 3: 28 / 28
• Subtask 4: 0 / 20
• Subtask 5: 0 / 30