Submission #233634

#	Time	Username	Problem	Language	Result	Execution time	Memory
233634		dolphingarlic	Islands (IOI08_islands)	C++14	100 / 100	1022 ms	131072 KiB

islands

#include <bits/stdc++.h>
 
using namespace std;
 
const int N = 1000005;
const long long INF = 1e18;
 
int n;
int par[N];
int deg[N];
int a[N], w[N];
long long mx, res;
long long f[N], g[N];
long long sum[N];
vector<int> G[N], vec[N];
 
int find(int u) { return u == par[u] ? u : par[u] = find(par[u]); }
 
void join(int u, int v) { par[find(u)] = find(v); }
 
void solve(vector<int> &vec) {
	queue<int> qu;
	for (auto i : vec) {
		deg[i] = G[i].size();
		if (!deg[i]) qu.push(i);
	}
	while (qu.size()) {
		int u = qu.front(); qu.pop();
		if (!--deg[a[u]]) qu.push(a[u]);
		f[a[u]] = max(f[a[u]], f[u] + w[u]);
 
	}
	vector<int> cir;
	for (auto i : vec) {
		if (!deg[i]) continue;
		int u = i, prv = 0;
		while (1) {
			cir.push_back(u), u = a[u];
			if (u == i) break;
		}
		break;
	}
	mx = 0;
	for (auto i : cir) {
		stack<int> st; st.push(i);
		while (st.size()) {
			int u = st.top(); st.pop();
			mx = max(mx, max(f[u], g[u]));
			long long mx1, mx2;
			mx1 = mx2 = -INF;
			for (auto v : G[u]) {
				if (deg[v]) continue;
				if (mx1 < f[v] + w[v]) mx2 = mx1, mx1 = f[v] + w[v];
				else if (mx2 < f[v] + w[v]) mx2 = f[v] + w[v];
			}
			for (auto v : G[u]) {
				if (deg[v]) continue;
				g[v] = g[u] + w[v];
				if (mx1 == f[v] + w[v]) g[v] = max(g[v], mx2 + w[v]);
				else g[v] = max(g[v], mx1 + w[v]);
				st.push(v);
			}
		}
	}
	int sz = cir.size();
	for (int i = 1; i <= sz; ++i) {
		sum[i] = sum[i - 1] + w[cir[i - 1]];
	}
	long long mx1 = -INF, mx2 = -INF;
	for (int i = 1; i <= sz; ++i) {
		int u = cir[i - 1];
		mx = max(mx, f[u] + sum[i - 1] + mx1);
		mx = max(mx, f[u] - sum[i - 1] + sum[sz] + mx2);
		mx1 = max(mx1, f[u] - sum[i - 1]);
		mx2 = max(mx2, f[u] + sum[i - 1]);
	}
	res += mx;
}
 
int main() {
	ios::sync_with_stdio(false);
	cin >> n;
	for (int i = 1; i <= n; ++i) par[i] = i;
	for (int i = 1; i <= n; ++i) {
		cin >> a[i] >> w[i];
		join(i, a[i]), G[a[i]].push_back(i);
	}
	for (int i = 1; i <= n; ++i) vec[find(i)].push_back(i);
	for (int i = 1; i <= n; ++i) if (find(i) == i) solve(vec[find(i)]);
	cout << res;
}

Compilation message (stderr)

islands.cpp: In function 'void solve(std::vector<int>&)':
islands.cpp:36:14: warning: unused variable 'prv' [-Wunused-variable]
   int u = i, prv = 0;
              ^~~

• 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: 10 / 10