Submission #756974

#	Time	Username	Problem	Language	Result	Execution time	Memory
756974		SanguineChameleon	Islands (IOI08_islands)	C++17	80 / 100	496 ms	131072 KiB

islands

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

void just_do_it();

int main() {
	#ifdef KAMIRULEZ
		freopen("kamirulez.inp", "r", stdin);
		freopen("kamirulez.out", "w", stdout);
	#endif
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	just_do_it();
	return 0;
}

struct root {
	int u, len;
	long long max_depth;

	root(): u(0), len(0), max_depth(0) {};

	root(int _u, int _len): u(_u), len(_len), max_depth(0) {};
};

const int maxn = 1e6 + 20;
vector<pair<int, int>> adj[maxn];
pair<int, int> par[maxn];
int len[maxn];
int depth[maxn];
pair<long long, int> max_depth[maxn];
bool flag[maxn];
bool is_cycle[maxn];
vector<root> cycle;

void dfs1(int u) {
	flag[u] = true;
	for (auto e: adj[u]) {
		int v = e.first;
		int id = e.second;
		if (id == par[u].second) {
			continue;
		}
		if (!flag[v]) {
			depth[v] = depth[u] + 1;
			par[v] = make_pair(u, id);
			dfs1(v);
		}
		else {
			if (depth[u] > depth[v]) {
				int cur = u;
				while (cur != v) {
					cycle.emplace_back(cur, len[par[cur].second]);
					cur = par[cur].first;
				}
				cycle.emplace_back(v, len[id]);
			}
		}
	}
}

void dfs2(int u, int p) {
	max_depth[u] = make_pair(0, u);
	for (auto e: adj[u]) {
		int v = e.first;
		int id = e.second;
		if (v != p && !is_cycle[v]) {
			dfs2(v, u);
			max_depth[u] = max(max_depth[u], make_pair(max_depth[v].first + len[id], max_depth[v].second));
		}
	}
}

long long solve() {
	int n = cycle.size();
	for (int i = 0; i < n; i++) {
		is_cycle[cycle[i].u] = true;
	}
	long long res = 0;
	for (int i = 0; i < n; i++) {
		int u = cycle[i].u;
		is_cycle[u] = false;
		dfs2(u, -1);
		cycle[i].max_depth = max_depth[u].first;
		int v = max_depth[u].second;
		dfs2(v, -1);
		res = max(res, max_depth[v].first);
		is_cycle[u] = true;
	}
	vector<long long> dist(n);
	long long mx = cycle[0].max_depth;
	for (int i = 1; i < n; i++) {
		dist[i] = dist[i - 1] + cycle[i - 1].len;
		res = max(res, dist[i] + cycle[i].max_depth + mx);
		mx = max(mx, cycle[i].max_depth - dist[i]);
	}
	long long sum = dist[n - 1] + cycle[n - 1].len;
	mx = cycle[0].max_depth;
	for (int i = 1; i < n; i++) {
		res = max(res, (sum - dist[i]) + cycle[i].max_depth + mx);
		mx = max(mx, cycle[i].max_depth + dist[i]);
	}
	return res;
}

void just_do_it() {
	int n;
	cin >> n;
	for (int u = 1; u <= n; u++) {
		int v;
		cin >> v >> len[u];
		adj[u].emplace_back(v, u);
		adj[v].emplace_back(u, u);
	}
	long long res = 0;
	for (int u = 1; u <= n; u++) {
		if (!flag[u]) {
			cycle.clear();
			par[u] = make_pair(-1, -1);
			dfs1(u);
			res += solve();
		}
	}
	cout << res;
}

• 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