Submission #439958

#	Time	Username	Problem	Language	Result	Execution time	Memory
439958		dutch	Islands (IOI08_islands)	C++17	12 / 100	783 ms	131076 KiB

islands

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

const int LIM = 1e6;

vector<array<int, 2>> a(LIM), g[LIM];
int r, p[LIM], dfsTimer, t0[LIM], t1[LIM];
ll best, d[LIM], s[LIM], pre[2*LIM], suf[2*LIM];
bitset<LIM> vis;

void dfs(int u, int par){
	p[u] = par, s[u] = -1;
	t0[u] = dfsTimer++;
	ll curr = 0;
	for(auto &[v, w] : g[u]) if(v != par && v != r){
		d[v] = d[u] + (ll)w, dfs(v, u);
		s[u] = max(s[u], s[v]);
		best = max(best, curr + s[v] - d[u]);
		curr = max(curr, s[v] - d[u]);
	}
	t1[u] = dfsTimer++;
	pre[t0[u]] = suf[t0[u]] = 0;
	pre[t1[u]] = suf[t1[u]] = 0;
	if(t0[u] + 1 == t1[u]) pre[t0[u]] = suf[t0[u]] = s[u] = d[u];
}

void findCycle(int u, int par){
	vis[u] = 1;
	for(auto &[v, w] : g[u]) if(v != par){
		if(vis[v]) return void(r = v);
		findCycle(v, u);
		if(r >= 0) return;
	}
	vis[u] = 0;
}

int main(){
	ios_base::sync_with_stdio(0); cin.tie(0);
	int n; cin >> n;

	for(int i=0; i<n; ++i){
		cin >> a[i][0] >> a[i][1];
		g[--a[i][0]].push_back({i, a[i][1]});
	}
	fill(p, p+n, -1);

	ll ans = 0;

	for(int z=0; z<n; ++z){
		if(p[z] >= 0) continue;
		r = -1;
		best = 0;
		findCycle(z, z);
		bool cycle = r >= 0;
		if(!cycle) r = z;

		dfsTimer = 0;
		dfs(r, r);
		if(!cycle){
			ans += best;
			continue;
		}
		for(int i=1; i<dfsTimer; ++i) pre[i] = max(pre[i], pre[i-1]);
		for(int i=dfsTimer-2; i>=0; --i) suf[i] = max(suf[i], suf[i+1]);

		int u = a[r][0], last = -1;
		ll res = 0, h = 0;
		while(u != r){
			ll mx = 0;
			for(auto &[v, w] : g[u]){
				if(v == last) h += w;
				else mx = max(mx, s[v] - d[u]);
			}
			ll ex = t0[u] ? pre[t0[u]-1] : 0LL;
			ex += t1[u]+1 < dfsTimer ? suf[t1[u]+1] : 0LL;
			res = max(res, h + mx + ex);
			last = u;
			u = p[u];
		}
		res = max(res, h);
		res += a[r][1];

		ans += max(best, res);
	}

	cout << ans;
}

• Subtask 1: 12 / 33
• Subtask 2: 0 / 3
• Subtask 3: 0 / 4
• Subtask 4: 0 / 10
• Subtask 5: 0 / 10
• Subtask 6: 0 / 10
• Subtask 7: 0 / 10
• Subtask 8: 0 / 10
• Subtask 9: 0 / 10