제출 #125125

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
125125		NMAC427	Islands (IOI08_islands)	C++17	0 / 100	378 ms	69228 KiB

islands

// https://oj.uz/problem/view/IOI08_islands

#include <bits/stdc++.h>
#define ff first
#define ss second

using namespace std;
using ll = long long int;

int N;

vector<pair<int, int>> to;
vector<vector<int>> from;
vector<bool> inCycle;

pair<ll, ll> dfsSolve(int v) {
	ll max1 = 0;
	ll max2 = 0;

	ll maxInternal = 0; // Maximum internal path;

	for (const int child: from[v]) {
		if (inCycle[child]) continue;  // Check here because we want to be able to pass in a node of the cycle

		auto childDFS = dfsSolve(child);
		childDFS.ff += to[child].ss;

		if (childDFS.ff >= max1) {
			max2 = max1;
			max1 = childDFS.ff;
		} else if (childDFS.ff > max2) {
			max2 = childDFS.ff;
		}

		maxInternal = max(maxInternal, childDFS.ss);
	}

	maxInternal = max(maxInternal, max1 + max2);
	return {max1, maxInternal};
}

signed main() {

	#ifndef __APPLE__
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	#endif

	cin >> N;

	to.resize(N);
	from.resize(N);

	for (int i = 0; i < N; i++) {
		cin >> to[i].ff >> to[i].ss;
		to[i].ff -= 1;

		from[to[i].ff].push_back(i);
	}


	// Generate inCycle Vector
	inCycle.assign(N, false);
	vector<bool> visited (N, false);

	for (int i = 0; i < N; i++) {
		if (visited[i]) continue;

		vector<int> cycle;
		int next = i;

		while (true) {
			visited[next] = true;
			cycle.push_back(next);

			if (visited[to[next].ff]) {
				bool __inCycle = false;
				for (int v: cycle)  {
					if (to[next].ff == v) __inCycle = true;
					if (__inCycle) inCycle[v] = true;
				}

				break;
			} else {
				next = to[next].ff;
			}
		}
	}

	from.clear();
	visited.clear();


	// Solve
	ll ans = 0;

	// for (int i = 0; i < N; i++) {
	// 	if (!inCycle[i]) continue;

	// 	ll compAns = 0;

	// 	vector<int> cycle;
	// 	vector<ll> dfsV;
	// 	vector<ll> prefixSum = {0};
	// 	int next = i;

	// 	do {
	// 		auto dfs = dfsSolve(next);
	// 		compAns = max(compAns, dfs.ss);  // Internal Path

	// 		cycle.push_back(next);
	// 		dfsV.push_back(dfs.ff);
	// 		prefixSum.push_back(prefixSum.back() + to[next].ss);
	// 		next = to[next].ff;
	// 	} while (next != i);

	// 	for (int v: cycle) {
	// 		inCycle[v] = false;  // Don't visit same component twice
	// 	}


	// 	ll prefixFwd = dfsV[0];
	// 	ll prefixBwd = dfsV[0];

	// 	for(int i = 1; i < cycle.size(); i++) {
	// 	 	compAns = max(compAns, dfsV[i] + prefixSum[i] + prefixFwd);
	// 	 	compAns = max(compAns, dfsV[i] - prefixSum[i] + prefixBwd + prefixSum.back());
		 	
	// 	 	prefixFwd = max(prefixFwd, dfsV[i] - prefixSum[i]);
	// 	 	prefixBwd = max(prefixBwd, dfsV[i] + prefixSum[i]);
	// 	}

	// 	ans += compAns;
	// }

	cout << ans << "\n";

	return 0;
}

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