Submission #1056531

#	Time	Username	Problem	Language	Result	Execution time	Memory
1056531		lovrot	Islands (IOI08_islands)	C++17	80 / 100	286 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, deg[N], to[N], weg[N]; 
vector<pii> g[N];

int cyci;
pii cyc[N];

void push_back(pii a) { 
	cyc[cyci++] = a;
}

void clear() {
	cyci = 0;
}

char bio[N];

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]) { 
				push_back({e.X, weg[e.Y]});
//				cyc.PB({e.X, weg[e.Y]});
				return v;
			} else {
				int res = dfs(v, w);
				if(res) { 
					push_back({e.X, weg[e.Y]});					
//					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) { 
		scanf("%d%d", to + i, weg + i);
		++deg[i];
		++deg[to[i]];
	}

	for(int i = 1; i <= n; ++i) { 
		g[i].reserve(deg[i]);
	}

	for(int i = 1; i <= n; ++i) {
		g[i].PB({to[i], i});
		g[to[i]].PB({i, i});
	}

	ll prf, prf_, len, ans = 0;
	int v, w;

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

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

		for(int j = 0; j < cyci; ++j) { 
			depth(cyc[j].X, 0);
			debug("%d(%d, %lld)\n", e.X, e.Y, dep[e.X]);
		}

		mark(i);
		
		prf = 0;
		for(int j = 0; j < cyci; ++j) { 
			v = cyc[j].X;
			w = cyc[j].Y;	
			s.insert(dep[v] + prf);
			prf += w;
		}

		prf_ = 0;
		len = prf;
		for(int j = 0; j < cyci; ++j) { 
			v = cyc[j].X;
			w = cyc[j].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:106:10: warning: variable 'prf_' set but not used [-Wunused-but-set-variable]
  106 |  ll prf, prf_, len, ans = 0;
      |          ^~~~
islands.cpp:89:7: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   89 |  scanf("%d", &n);
      |  ~~~~~^~~~~~~~~~
islands.cpp:92:8: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   92 |   scanf("%d%d", to + i, weg + i);
      |   ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

• 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