Submission #440006

#	Time	Username	Problem	Language	Result	Execution time	Memory
440006		dutch	Islands (IOI08_islands)	C++17	40 / 100	433 ms	131076 KiB

islands

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
 
const int LIM = 1e6;
 
vector<array<int, 3>> g[LIM];
array<int, 2> a[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){
	s[u] = d[u];
	t0[u] = dfsTimer++;
	ll curr = 0;
	for(auto &[v, w, e] : g[u]) if(e != par && v != r){
		d[v] = d[u] + (ll)w, p[v] = u;
		dfs(v, e);
		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]] = d[u];
	pre[t1[u]] = suf[t1[u]] = 0;
}
 
void findCycle(int u, int par){
	vis[u] = 1;
	for(auto &[v, w, e] : g[u]) if(e != par){
		if(vis[v]) return void(r = v);
		findCycle(v, e);
		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]; --a[i][0];
		g[a[i][0]].push_back({i, a[i][1], i});
		g[i].push_back({a[i][0], a[i][1], i});
	}
	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;
		}
		assert(cycle);
 
		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;
		while(u != r){
			ll mx = 0;
			for(auto &[v, w, e] : g[u])
				if(v != p[u] && v != last) mx = max(mx, s[v] - d[u]);
 
			ll ex = 0;
 
			if(t0[u]) ex = max(ex, pre[t0[u]-1]);
			if(t1[u] + 1 < dfsTimer) ex = max(ex, suf[t1[u]+1]);
			res = max(res, d[a[r][0]] - d[u] + mx + ex);
			last = u;
			u = p[u];
		}
		res += a[r][1];

		ans += max(best, res);
	}
 
	cout << ans;
}

• Subtask 1: 27 / 33
• Subtask 2: 3 / 3
• Subtask 3: 0 / 4
• Subtask 4: 0 / 10
• Subtask 5: 10 / 10
• Subtask 6: 0 / 10
• Subtask 7: 0 / 10
• Subtask 8: 0 / 10
• Subtask 9: 0 / 10