Submission #396300

#	Time	Username	Problem	Language	Result	Execution time	Memory
396300		Berted	Islands (IOI08_islands)	C++14	80 / 100	1138 ms	131076 KiB

islands

#include <iostream>
#include <vector>
#include <algorithm>
#include <deque>
#include <fstream>
#define ll long long
#define pii pair<int, int>
#define fst first
#define snd second
 
using namespace std;
 
int N;
vector<pii> adj[1000001];
int H[1000001]; vector<int> vis;
vector<pii> cyc;
ll DP[1000001], D2[1000001];
deque<pair<ll, int>> dq;
 
ll tmp[2], ans = 0;
 
inline int DFS1(int u, pii p)
{
	int ret = H[u] + 1;
	vis.push_back(u);
 
	//cerr << "D1: " << u << " " << H[u] << "\n";
	for (const pii &v : adj[u])
	{
		if (p == v) {p = {-1, -1}; continue;}
		if (H[v.fst] == -1)
		{
			H[v.fst] = H[u] + 1;
			ret = DFS1(v.fst, {u, v.snd});
		}
		else if (H[v.fst] < H[u]) {ret = H[v.fst];}
		if (ret <= H[u])
		{
			cyc.push_back({u, v.snd});
			break;
		}
	}
	return ret;
}
 
inline void DFS2(int u)
{
	for (const pii &v : adj[u])
	{
		if (H[v.fst] == -1)
		{
			H[v.fst] = H[u] + 1;
			DFS2(v.fst);
			D2[u] = max(D2[u], D2[v.fst]);
			DP[u] = max(DP[u], DP[v.fst] + v.snd);
		}
	}
	tmp[0] = tmp[1] = 0;
	for (const pii &v : adj[u])
	{
		if (H[v.fst] > H[u])
		{
			if (DP[v.fst] + v.snd > tmp[0]) {tmp[1] = tmp[0]; tmp[0] = DP[v.fst] + v.snd;}
			else if (DP[v.fst] + v.snd > tmp[1]) {tmp[1] = DP[v.fst] + v.snd;}
		}
	}
	D2[u] = max(D2[u], tmp[0] + tmp[1]);
}
 
int main()
{
	ios :: sync_with_stdio(0); cin.tie(0); cout.tie(0);
	cin >> N;
	for (int i = 0; i < N; i++)
	{
		int u, c; cin >> u >> c; u--;
		adj[u].push_back({i, c});
		adj[i].push_back({u, c});
		H[i] = -1;
	}

	//cerr << "adj\n";
 
	for (int k = 0; k < N; k++)
	{
		if (H[k] == -1)
		{
			ll rr = 0; H[k] = 0;
			DFS1(k, {-1, -1});

			//cerr << "D1done\n";

			for (const auto &u : vis) H[u] = -1;
			vis.clear();
			
			for (const auto &u : cyc) H[u.fst] = 0;
			for (const auto &u : cyc) {DFS2(u.fst); rr = max(rr, D2[u.fst]);}
 
			//cerr << k << ": " << rr << " " << cyc.size() << "\n";
 
			ll s = 0, t = 0;
			for (int i = 1; i < cyc.size(); i++)
			{
				//cerr << "id: " << i << " " << cyc[i].fst << " - " << DP[cyc[i].fst] << "\n";
				s += cyc[i].snd;
				while (dq.size() && dq.back().fst <= s + DP[cyc[i].fst]) 
				{
					//cerr << "Popped\n";
					dq.pop_back();
				}
				//cerr << "Pushed: " << s + DP[cyc[i].fst] << ", " << i << "\n";
				dq.push_back({s + DP[cyc[i].fst], i});
			}
			s += cyc[0].snd;
 
			for (int i = 0; i < cyc.size(); i++)
			{
				if (dq.front().snd == i) dq.pop_front();
				//cerr << i << " " << " " << cyc[i].fst << " " << dq.front().fst << " " << t << " " << DP[cyc[i].fst] << "\n";
				rr = max(rr, dq.front().fst + t + DP[cyc[i].fst]);
				while (dq.size() && dq.back().fst + t <= s + DP[cyc[i].fst]) {dq.pop_back();}
				dq.push_back({s + DP[cyc[i].fst] - t, i});
				t -= cyc[(i + 1) % cyc.size()].snd;
			}
 
			dq.clear();
			cyc.clear();
 
			//cerr << k << ": " << rr << "\n";
 
			ans += rr;
		}
	}
	
	cout << ans << "\n";
	return 0;
}

Compilation message (stderr)

islands.cpp: In function 'int main()':
islands.cpp:102:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  102 |    for (int i = 1; i < cyc.size(); i++)
      |                    ~~^~~~~~~~~~~~
islands.cpp:116:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  116 |    for (int i = 0; i < cyc.size(); i++)
      |                    ~~^~~~~~~~~~~~

• Subtask 1: 33 / 33
• Subtask 2: 3 / 3
• Subtask 3: 4 / 4
• Subtask 4: 10 / 10
• Subtask 5: 10 / 10
• Subtask 6: 10 / 10
• Subtask 7: 10 / 10
• Subtask 8: 0 / 10
• Subtask 9: 0 / 10