Submission #440035

#	Time	Username	Problem	Language	Result	Execution time	Memory
440035		dutch	Islands (IOI08_islands)	C++17	80 / 100	1187 ms	131076 KiB

islands

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define w (a[e][1])
#define V() (e == u ? a[e][0] : e)
#define v V()
 
const int LIM = 1e6;

vector<int> g[LIM];
array<int, 2> a[LIM];
int r, p[LIM];
ll b[LIM], d[LIM], s[LIM], best;
bitset<LIM> vis;
 
void dfs(int u){
	vis[u] = 1, s[u] = d[u];
	ll curr = 0;
	for(int e : g[u]) if(e != r && !vis[v]){
		p[v] = u;
		d[v] = d[u] + (ll)w;
		dfs(v);
		s[u] = max(s[u], s[v]);
		best = max(best, curr + s[v] - d[u]);
		curr = max(curr, s[v] - d[u]);
	}
}
 
void findCycle(int u, int par){
	vis[u] = 1;
	for(int e : g[u]) if(e != par){
		if(vis[v]) return void(r = e + (vis[u] = 0));
		findCycle(v, e);
		if(r >= 0) break;
	}
	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);
		g[i].push_back(i);
	}
	fill(p, p+n, -1);
 
	ll ans = 0;
 
	for(int z=0; z<n; ++z){
		if(vis[z]) continue;
		r = -1, best = 0;
		findCycle(z, -1);
		assert(r >= 0);
		dfs(r);

		function<void(int, int)> find = [&](int u, int last){
			b[u] = d[u];
			for(int e : g[u])
				if(e != r && v != p[u] && v != last) b[u] = max(b[u], s[v]);

			if(u != r){
				find(p[u], u);
				b[u] = max(b[u], b[p[u]]);
			}
		};
		find(a[r][0], -1);

		int u = a[r][0], last = -1;
		ll res = 0;

		while(u != r){
			ll mx = 0, ex = 0;
			for(int e : g[u])
				if(e != r && v != p[u] && v != last) mx = max(mx, s[v] - d[u]);

			res = max(res, d[a[r][0]] - d[u] + mx + b[p[u]]);
			last = u;
			u = p[u];
		}
		res += a[r][1];
 		// cout << r+1 << ' ' << best << ' ' << res << '\n';
		ans += max(best, res);
	}
 
	cout << ans;
}

Compilation message (stderr)

islands.cpp: In function 'int main()':
islands.cpp:75:15: warning: unused variable 'ex' [-Wunused-variable]
   75 |    ll mx = 0, ex = 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: 0 / 10
• Subtask 9: 0 / 10