Submission #151534

#	Time	Username	Problem	Language	Result	Execution time	Memory
151534		luciocf	Islands (IOI08_islands)	C++14	90 / 100	1626 ms	131076 KiB

islands

#include <bits/stdc++.h>

using namespace std;

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

const int maxn = 1e6+10;
const ll inf = 1e18+10;

int n;

int peso[maxn];

int firstCycle, lastCycle, backEdge;
int pai[maxn], indCycle[maxn], edgePai[maxn];

ll pref[maxn];
ll maiorDist[maxn], maiorDist2;
int indDist;

bool mark[maxn], markCycle[maxn];

vector<pii> grafo[maxn];

void findCycle(int u, int p)
{
	mark[u] = 1;

	for (auto pp: grafo[u])
	{
		int v = pp.first, e = pp.second;
		if (e == p) continue;

		if (mark[v])
		{
			firstCycle = u, lastCycle = v;
			backEdge = peso[e];
			continue;
		}

		pai[v] = u, edgePai[v] = peso[e];
		findCycle(v, e);
	}
}

void dfs(int u, int p, int root, ll dist)
{
	if (dist >= maiorDist[root])
		indDist = u;

	maiorDist[root] = max(maiorDist[root], dist);

	for (auto pp: grafo[u])
	{
		int v = pp.first, e = pp.second;
		if (v == p || markCycle[v]) continue;

		dfs(v, u, root, dist+1ll*peso[e]);
	}
}

void dfs2(int u, int p, ll dist)
{
	maiorDist2 = max(maiorDist2, dist);

	for (auto pp: grafo[u])
	{
		int v = pp.first, e = pp.second;
		if (v == p || markCycle[v]) continue;

		dfs2(v, u, dist+1ll*peso[e]);
	}
}

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

	for (int i = 1; i <= n; i++)
	{
		int u, w;
		scanf("%d %d", &u, &w);

		peso[i] = w;

		grafo[u].push_back({i, i});
		grafo[i].push_back({u, i});
	}

	ll ans = 0;
	vector<int> ciclo;

	for (int T = 1; T <= n; T++)
	{
		if (mark[T]) continue;

		findCycle(T, 0);

		int at = lastCycle;
		ll soma = backEdge;

		ciclo.clear();

		while (true)
		{
			ciclo.push_back(at);
			markCycle[at] = 1;

			if (at == firstCycle) break;

			soma += 1ll*edgePai[at];
			at = pai[at];
		}

		reverse(ciclo.begin(), ciclo.end());

		ll M = 0, diam = 0;

		for (int i = 0; i < ciclo.size(); i++)
		{
			int c = ciclo[i];

			if (i > 0)
				pref[i] = pref[i-1] + 1ll*edgePai[c];

			dfs(c, 0, c, 0);

			maiorDist2 = 0;
			markCycle[c] = 0;

			dfs2(indDist, 0, 0);
			markCycle[c] = 1;

			diam = max(diam, maiorDist2);
		}

		ll maxi1 = -inf, maxi2 = -inf;
		for (int i = 0; i < ciclo.size(); i++)
		{
			int u = ciclo[i];

			M = max(M, maiorDist[u]+pref[i] + maxi1);
			maxi1 = max(maxi1, maiorDist[u]-pref[i]);

			M = max(M, maiorDist[u]-pref[i] + maxi2 + soma);

			maxi2 = max(maxi2, maiorDist[u]+pref[i]);
		}

		ans += max(M, diam);
	}

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

Compilation message (stderr)

islands.cpp: In function 'int main()':
islands.cpp:120:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int i = 0; i < ciclo.size(); i++)
                   ~~^~~~~~~~~~~~~~
islands.cpp:139:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int i = 0; i < ciclo.size(); i++)
                   ~~^~~~~~~~~~~~~~
islands.cpp:78:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d", &n);
  ~~~~~^~~~~~~~~~
islands.cpp:83:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d %d", &u, &w);
   ~~~~~^~~~~~~~~~~~~~~~~

• 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: 10 / 10
• Subtask 9: 0 / 10