Submission #757039

#	Time	Username	Problem	Language	Result	Execution time	Memory
757039		SanguineChameleon	Islands (IOI08_islands)	C++17	90 / 100	848 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;
}

const int maxn = 1e6 + 20;
int to[maxn];
pair<int, int> edges[maxn * 2];
int adj_pt[maxn];
int par[maxn];
int len[maxn];
long long dp[maxn];
bool flag[maxn];
bool is_cycle[maxn];
int cycle[maxn];
bool head[maxn];
int sz;

void dfs1(int u) {
	flag[u] = true;
	for (int pt = adj_pt[u]; edges[pt].first == u; pt++) {
		int id = edges[pt].second;
		if (id == par[u]) {
			continue;
		}
		int v = id ^ to[id] ^ u;
		if (!flag[v]) {
			par[v] = id;
			dfs1(v);
		}
		else {
			int cur = u;
			while (cur != v) {
				if (par[cur] == -1) {
					break;
				}
				cur = par[cur] ^ to[par[cur]] ^ cur;
			}
			if (cur == v) {
				cur = u;
				while (cur != v) {
					cycle[sz] = cur;
					head[sz] = (par[cur] == cur);
					sz++;
					cur = par[cur] ^ to[par[cur]] ^ cur;
				}
				cycle[sz] = v;
				head[sz] = (id == v);
				sz++;
			}
		}
	}
}

long long res;

void dfs2(int u, int p) {
	dp[u] = 0;
	long long mx1 = 0;
	long long mx2 = 0;
	for (int pt = adj_pt[u]; edges[pt].first == u; pt++) {
		int id = edges[pt].second;
		int v = id ^ to[id] ^ u;
		if (v != p && !is_cycle[v]) {
			dfs2(v, u);
			dp[u] = max(dp[u], dp[v] + len[id]);
			if (dp[v] + len[id] > mx1) {
				mx2 = mx1;
				mx1 = dp[v] + len[id];
			}
			else if (dp[v] + len[id] > mx2) {
				mx2 = dp[v] + len[id];
			}
		}
	}
	res = max(res, mx1 + mx2);
}

long long calc_max(int u) {
	is_cycle[u] = false;
	dfs2(u, -1);
	is_cycle[u] = true;
	return dp[u];
}

long long solve() {
	res = 0;
	long long sum = 0;
	for (int i = 0; i < sz; i++) {
		is_cycle[cycle[i]] = true;
		sum += (head[i] ? len[cycle[i]] : len[cycle[(i + 1) % sz]]);
	}
	long long dist = 0;
	long long mx1 = calc_max(cycle[0]);
	long long mx2 = mx1;
	for (int i = 1; i < sz; i++) {
		dist += (head[i - 1] ? len[cycle[i - 1]] : len[cycle[i]]);
		long long max_depth = calc_max(cycle[i]);
		res = max(res, dist + max_depth + mx1);
		res = max(res, sum - dist + max_depth + mx2);
		mx1 = max(mx1, max_depth - dist);
		mx2 = max(mx2, max_depth + dist);
	}
	return res;
}

void just_do_it() {
	int n;
	cin >> n;
	for (int i = 1; i <= n; i++) {
		cin >> to[i] >> len[i];
		edges[i * 2 - 1].first = i;
		edges[i * 2 - 1].second = i;
		edges[i * 2].first = to[i];
		edges[i * 2].second = i;
	}
	sort(edges + 1, edges + n * 2 + 1);
	for (int i = 1; i <= n * 2; i++) {
		if (edges[i].first != edges[i - 1].first) {
			adj_pt[edges[i].first] = i;
		}
	}
	long long res = 0;
	for (int u = 1; u <= n; u++) {
		if (!flag[u]) {
			sz = 0;
			par[u] = -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: 10 / 10
• Subtask 9: 0 / 10