Submission #1055281

#	Time	Username	Problem	Language	Result	Execution time	Memory
1055281		lovrot	Islands (IOI08_islands)	C++17	12 / 100	185 ms	131072 KiB

islands

#include <cstdio> 
#include <vector>
#include <algorithm> 
#include <set>

#define debug(...) //fprintf(stderr, __VA_ARGS__)
#define X first
#define Y second
#define PB push_back

using namespace std;

typedef long long ll;
typedef pair<int, int> pii;

const int N = 1e6 + 10;

int n, weg[N]; 
vector<pii> g[N];

char bio[N];
vector<pii> cyc;

int dfs(int u, int p) { 
	bio[u] = 1;
	for(pii e : g[u]) { 
		int v = e.X, w = e.Y;
		if(w != p) { 
			if(bio[v]) { 
				cyc.PB({e.X, weg[e.Y]});
				return v;
			} else {
				int res = dfs(v, w);
				if(res) { 
					cyc.PB({e.X, weg[e.Y]});
					return res != u ? res : 0;
				}
			}
		}
	}
	bio[u] = 0;
	return 0;
}

void mark(int u) { 
	bio[u] = 2;
	for(pii e : g[u]) { 
		if(bio[e.X] != 2) { 
			mark(e.X);
		}
	}
}

ll dep[N], ans_;

ll depth(int u, int p) { 
	ll max_ = 0;
	for(pii e : g[u]) { 
		int v = e.X, w = e.Y;
		if(w != p && !bio[v]) { 
			ll res = (ll) weg[w] + depth(v, w);
			if(dep[u] < res) { 
				max_ = dep[u]; 
				dep[u] = res;
			} else if(max_ < res) { 
				max_ = res;
			}
		}
	}
	ans_ = max(ans_, dep[u] + max_);
	return dep[u];
}

multiset<ll> s;

int main() { 
	scanf("%d", &n);

	for(int i = 1; i <= n; ++i) { 
		int u;
		scanf("%d%d", &u, weg + i);
		g[i].PB({u, i});
		g[u].PB({i, i});
	}

	ll ans = 0;
	for(int i = 1; i <= n; ++i) { 
		if(bio[i]) { continue; }

		cyc.clear();
		s.clear();
		ans_ = 0;
		dfs(i, 0);

		for(pii e : cyc) { 
//			depth(e.X, 0);
			debug("%d(%d, %lld)\n", e.X, e.Y, dep[e.X]);
		}

		mark(i);

		ll prf = 0;
		for(pii e : cyc) { 
			int v = e.X, w = e.Y;	
			s.insert(dep[v] + prf);
			prf += w;
		}

		ll prf_ = 0, len = prf;
		for(pii e : cyc) {
			int v = e.X, w = e.Y;
			s.erase(s.find(dep[v] + prf - len));

			ans_ = max(ans_, *prev(s.end()) + dep[v] - prf + len);

			s.insert(dep[v] + prf);
			prf += w;
		}

		ans += ans_;
	}

	printf("%lld\n", ans);
	return 0;
}

Compilation message (stderr)

islands.cpp: In function 'int main()':
islands.cpp:95:11: warning: variable 'e' set but not used [-Wunused-but-set-variable]
   95 |   for(pii e : cyc) {
      |           ^
islands.cpp:109:6: warning: unused variable 'prf_' [-Wunused-variable]
  109 |   ll prf_ = 0, len = prf;
      |      ^~~~
islands.cpp:77:7: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   77 |  scanf("%d", &n);
      |  ~~~~~^~~~~~~~~~
islands.cpp:81:8: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   81 |   scanf("%d%d", &u, weg + i);
      |   ~~~~~^~~~~~~~~~~~~~~~~~~~~

• 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