Submission #1083287

#	Time	Username	Problem	Language	Result	Execution time	Memory
1083287		Math4Life2020	Ancient Books (IOI17_books)	C++17	50 / 100	106 ms	46196 KiB

books

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

using ll = long long; using pii = pair<ll,ll>;
const ll INF = 1e18;
//#include "books.h"

ll minimum_walk(vector<int> p, int s) {
	ll N = p.size();
	ll flux[N];
	for (ll i=0;i<N;i++) {
		flux[i]=0;
	}
	for (ll i=0;i<N;i++) {
		if (p[i]>i) {
			flux[i]++;
			flux[p[i]]--;
		}
	}
	ll pf[N+1];
	pf[0]=0;
	ll ans = 0;
	for (ll i=0;i<N;i++) {
		pf[i+1]=pf[i]+flux[i];
		//cout << "x="<<(i+1)<<", pf[x]="<<pf[i+1]<<"\n";
		if (pf[i+1]>1) {
			ans += 2*(pf[i+1]-1);
		}
	}
	ll maxl[N+1]; ll minl[N+1];
	for (ll i=0;i<=N;i++) {
		maxl[i]=-INF;
		minl[i]=INF;
	}
	for (ll i=1;i<=N;i++) {
		maxl[pf[i]]=max(maxl[pf[i]],i);
		minl[pf[i]]=min(minl[pf[i]],i-1);
	}
	for (ll i=N;i>=1;i--) {
		maxl[i-1]=max(maxl[i],maxl[i-1]);
		minl[i-1]=min(minl[i],minl[i-1]);
	}
	if (minl[1]!=INF) { //below valid if s=0
		ans += 2*(maxl[1]-minl[1]);
	}
	if (minl[1]!=INF) { //below valid if s=0
		if (s==0) {
			ans += 2*(minl[1]);
		}
	}
	if (s != 0) {
		bool found[N];
		ll grp[N];
		bool grpf[N];
		vector<vector<ll>> gelem;
		bool foundg[N];
		bool found2[N];
		for (ll i=0;i<N;i++) {
			found[i]=0;
			grp[i]=-1;
			grpf[i]=0;
			foundg[i]=0;
			found2[i]=0;
		}
		for (ll i=0;i<N;i++) {
			if (!found[i]) {
				vector<ll> enew;
				//cout << "f1\n";
				ll j = i;
				ll T = 0;
				ll lp=INF; ll rp=-INF;
				do {
					T++;
					lp = min(lp,j);
					rp = max(rp,j);
					found[j]=1;
					enew.push_back(j);
					j=p[j];
				} while (j != i);
				for (ll x: enew) {
					grp[x]=gelem.size();
					//cout << "x="<<x<<", grp[x]="<<grp[x]<<"\n";
				}
				gelem.push_back(enew);
			}
		}
		priority_queue<pii> pq; //{-time,position}
		pq.push({0,s});
		ll Tmin = INF;
		while (!pq.empty()) {
			auto A = pq.top(); pq.pop();
			ll t = -A.first; ll x = A.second;
			if (found2[x]) {
				continue;
			}
			found2[x]=1;
			if (x==maxl[1] || x==minl[1]) {
				Tmin = min(Tmin,t);
			}
			ll g = grp[x];
			if (!foundg[g]) {
				foundg[g]=1;
				for (ll y: gelem[g]) {
					if (y != x) {
						pq.push({-t,y});
					}
				}
			}
			if (x>0) {
				pq.push({-t-1,x-1});
			}
			if (x<(N-1)) {
				pq.push({-t-1,x+1});
			}
		}
		ans += 2*Tmin;
	}
	//cout << "minl[1],maxl[1]="<<minl[1]<<","<<maxl[1]<<"\n";
	return ans;
}

/*int main() {
	vector<int> p1 = {0,1,4,3,2,5,6};
	cout << minimum_walk(p1,3);
}*/

Compilation message (stderr)

books.cpp: In function 'll minimum_walk(std::vector<int>, int)':
books.cpp:54:8: warning: variable 'grpf' set but not used [-Wunused-but-set-variable]
   54 |   bool grpf[N];
      |        ^~~~

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