Submission #834199

#	Time	Username	Problem	Language	Result	Execution time	Memory
834199		Josia	Ancient Books (IOI17_books)	C++17	12 / 100	1 ms	596 KiB

books

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

using namespace std;

#define int int64_t


vector<int> p;
int s;
int n;
int ret;

struct cycle {
	int left=1e9, right=-1e9;
	set<int> points;
};
bool CycleLess(cycle &a, cycle &b) {
	return pair<int, int>{a.left, a.right} < pair<int, int>{b.left, b.right};
}
bool merge(cycle &a, cycle &b) {			// a<-b
	if (!(a.left < b.left && a.right < b.right && a.right > b.left)) return 0;

	if (a.points.size() < b.points.size()) swap(a, b);

	a.right = b.right;
	for (int i: b.points) a.points.insert(i);
	
	return 1;
}
bool contains(cycle &a, cycle &b) {
	return (a.left <= b.left && b.right <= a.right);
}



vector<bool> vis;
cycle getCycle(int v) {
	assert(vis[v]==0);

	cycle res;

	while (vis[v] == 0) {
		vis[v] = 1;
		res.left = min(res.left, v);
		res.right = max(res.right, v);
		res.points.insert(v);

		ret += abs(v-p[v]);
		v = p[v];
	}
	return res;
}

vector<cycle> mergedCycles;
vector<int> parents;

int dfs(int v, int par) {
	parents[v] = par;
	int w = v+1;

	while (w<(int)mergedCycles.size() && contains(mergedCycles[v], mergedCycles[w])) {
		w = dfs(w, v);
	}
	return w;
}


void solve() {
	vis.assign(n, 0);

	vector<cycle> cycles;

	if (p[s]==s) cycles.push_back({s, s, {s}});
	int globLeft=s, globRight=s;

	for (int i = 0; i<n; i++) {
		if (vis[i]) continue;
		cycles.push_back(getCycle(i));
		if (cycles.back().left == cycles.back().right) cycles.pop_back();
		else {
			globLeft = min(globLeft, cycles.back().left);
			globRight = max(globRight, cycles.back().right);
		}
	}


	sort(cycles.begin(), cycles.end(), CycleLess);

	vector<int> inds;

	for (int i = 0; i<(int)(cycles.size())-1; i++) {
		if(merge(cycles[i+1], cycles[i])) continue;
		inds.push_back(i);
	}
	inds.push_back((int)(cycles.size())-1);

	mergedCycles.clear();
	// mergedCycles.push_back({globLeft, globRight, {globLeft, globRight}});
	for (int i: inds) mergedCycles.push_back(cycles[i]);


	parents.assign(mergedCycles.size(), -1);
	for (int i = 0; i<(int)mergedCycles.size(); i=dfs(i, -1));


	int pos=-1;
	for (int i = 0; i<(int)mergedCycles.size(); i++) {
		if (mergedCycles[i].points.count(s)) pos = i;
	}
	assert(pos!=-1);



	vector<pair<int, int>> jump(n);

	for (int i = 0; i<n; i++) {
		jump[i]={i, i};
	}

	for (int i: inds) {
		for (int j: cycles[i].points) {
			jump[j].first = cycles[i].left;
			jump[j].second = cycles[i].right;
		}
	}
	// return;

	// for(int i: parents) cerr << i << " ";
	// cerr << "\n";

	
	while (parents[pos] != -1) {
		cycle elem = mergedCycles[pos];
		cycle parent = mergedCycles[parents[pos]];

		auto goRightPoint = parent.points.lower_bound(elem.left);
		auto goLeftPoint = prev(parent.points.upper_bound(elem.right));

		assert(parent.points.lower_bound(elem.left) != parent.points.end());
		assert(parent.points.upper_bound(elem.right) != parent.points.begin());

		// let's hope it'll not go wrong.

		int right = *goRightPoint, left = *goLeftPoint;

		// if (right <= elem.right || left >= elem.left) {
		// 	pos = parents[pos];
		// 	continue;
		// }

		int costRight = 0;
		int posToRight = elem.right;
		while (posToRight < right) {
			costRight++;
			posToRight = jump[posToRight+1].second;
		}

		int costLeft = 0;
		int posToLeft = elem.left;
		while (posToLeft > left) {
			costLeft++;
			posToLeft = jump[posToLeft-1].first;
		}

		ret += 2*min(costLeft, costRight);

		pos = parents[pos];
	}

	vector<int> noParent;

	for (int i = 0; i<(int)parents.size(); i++) {
		if (parents[i] == -1) noParent.push_back(i);
	}

	for (int i = 0; i<(int)(noParent.size())-1; i++) {
		assert(mergedCycles[i+1].left>mergedCycles[i].right);
		ret+=2*(mergedCycles[i+1].left-mergedCycles[i].right);
	}
}


long long minimum_walk(vector<signed> _p, signed _s) {
	ret = 0;
	s = _s;
	n = _p.size();
	p.resize(n); for (int i = 0; i<n; i++) p[i] = _p[i];

	
	solve();


	return ret;
}

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