Submission #566451

#	Time	Username	Problem	Language	Result	Execution time	Memory
566451		sofapuden	Ancient Books (IOI17_books)	C++14	100 / 100	183 ms	34804 KiB

books

#include "books.h"
#include<bits/stdc++.h>

using namespace std;

typedef long long ll;

vector<pair<int,int>> segs;
vector<int> vis;

pair<int,int> getNext(int x, bool r){
	pair<int,int> bound = {x, x};
	if(r) {
		for(int i = x; i <= bound.second; ++i){
			bound.first = min(bound.first,segs[vis[i]].first);
			bound.second = max(bound.second,segs[vis[i]].second);
		}
	} else {
		for(int i = x; i >= bound.first; --i){
			bound.first = min(bound.first,segs[vis[i]].first);
			bound.second = max(bound.second,segs[vis[i]].second);
		}
	}
	return bound;
}

ll minimum_walk(vector<int> p, int s) {
	int n = p.size(), mx = 0, cn = 0;
	ll ans = 0;

	segs.resize(n+1,{n,0});
	vis.resize(n,0);

	for(int i = 0; i < n; ++i) {
		if(!vis[i]) {
			cn++;
			while(!vis[i]) {
				ans+=abs(i-p[i]);
				vis[i] = cn;
				i = p[i]; // goes back to original i
			}
		}
	}
	for(int i = 0; i < n; ++i) {
		segs[vis[i]].first = min(segs[vis[i]].first,i);
		segs[vis[i]].second = max(segs[vis[i]].second,i);
	}

	queue<int> Q;
	Q.push(s);
	int l = s, r = s;
	while(Q.size()){
		auto x = Q.front();
		Q.pop();
		for(int i = segs[vis[x]].first; i < l; ++i){
			Q.push(i);
		}
		for(int i = segs[vis[x]].second; i > r; --i){
			Q.push(i);
		}
		l = min(l,segs[vis[x]].first);
		r = max(r,segs[vis[x]].second);
	}
	int cnt = 0;
	int cua = 0, cub = 0;
	while(l || r < n-1){
		cnt++;
		pair<int,int> a = {r,r}, b = {l,l};
		if(r < n-1)a = getNext(r+1,1);
		if(l)b = getNext(l-1,0);
		if(a.first == a.second)cua++;
		else cua = 0;
		if(b.first == b.second)cub++;
		else cub = 0;
		if(a.first <= b.second){
			ans+=2*cnt;
			cnt = 0;
			cua = cub = 0;
		}
		pair<int,int> nbound = {min(a.first,b.first),max(a.second,b.second)};
		for(int i = nbound.first; i < l; ++i){
			Q.push(i);
		}
		for(int i = nbound.second; i > r; --i){
			Q.push(i);
		}
		while(Q.size()){
			auto x = Q.front();
			Q.pop();
			for(int i = segs[vis[x]].first; i < l; ++i){
				Q.push(i);
			}
			for(int i = segs[vis[x]].second; i > r; --i){
				Q.push(i);
			}
			l = min(l,segs[vis[x]].first);
			r = max(r,segs[vis[x]].second);
		}
	}
	ans+=4*cnt-2*(cua+cub);
	return ans;
}

Compilation message (stderr)

books.cpp: In function 'll minimum_walk(std::vector<int>, int)':
books.cpp:28:20: warning: unused variable 'mx' [-Wunused-variable]
   28 |  int n = p.size(), mx = 0, cn = 0;
      |                    ^~

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