제출 #151517

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
151517		luciocf	Islands (IOI08_islands)	C++14	18 / 100	562 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 dist[maxn], max1[maxn], max2[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)
{
	if (dist[u] >= maiorDist[root])
		indDist = u;

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

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

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

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

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

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

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;

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

		findCycle(T, 0);

		int at = lastCycle;
		ll soma = backEdge;

		vector<int> ciclo;

		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 (auto c: ciclo)
		{
			dfs(c, 0, c);

			dist[indDist] = maiorDist2 = 0;
			dfs2(indDist, 0);

			diam = max(diam, maiorDist2);
		}


		max1[ciclo.back()] = max2[ciclo.back()] = -inf;
		for (int i = ciclo.size()-2; i >= 0; i--)
		{
			int u = ciclo[i], v = ciclo[i+1];

			max1[u] = max(maiorDist[v], max1[v]) + 1ll*edgePai[v];

			max2[u] = max(soma-1ll*edgePai[v]+maiorDist[v], max2[v]-1ll*edgePai[v]);

			M = max(max1[u], max2[u]) + maiorDist[u];
		}

		ans += max(M, diam);
	}

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

컴파일 시 표준 에러 (stderr) 메시지

islands.cpp: In function 'int main()':
islands.cpp:80:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d", &n);
  ~~~~~^~~~~~~~~~
islands.cpp:85:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d %d", &u, &w);
   ~~~~~^~~~~~~~~~~~~~~~~

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