Submission #125088

#	Time	Username	Problem	Language	Result	Execution time	Memory
125088		NMAC427	Islands (IOI08_islands)	C++17	0 / 100	776 ms	131076 KiB

islands

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

#include <bits/stdc++.h>
#define coutV(v) for (auto &e: v) {cerr << e << " ";} cerr << "\n"
#define int int64_t
#define ff first
#define ss second

using namespace std;

int N;

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

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

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

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

	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);
	vector<int> __cycle;

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

		__cycle.clear();

		queue<int> q;
		q.push(i);

		while (!q.empty()) {
			auto front = q.front();
			q.pop();

			__cycle.push_back(front);

			if (visited[front]) {
				bool __inCycle = false;
				for (auto v: __cycle)  {
					if (to[i].ff == v) __inCycle = true;
					if (__inCycle) inCycle[v] = true;
				}

				continue;
			}

			visited[front] = true;
			q.push(to[front].ff);
		}
	}

	// Solve
	int ans = 0;

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

		int compAns = 0;

		int next = i;
		vector<int> cycle;
		vector<int> dfsV;

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

			cycle.push_back(next);
			dfsV.push_back(dfs.ff);
			next = to[next].ff;
		} while (next != i);

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

		coutV(cycle);

		int leftPtr = 0;
		int rightPtr = 1;
		int diameter = cycle.size();
		int prefix = dfsV[0] + to[i].ss;

		while (leftPtr < diameter && leftPtr != (rightPtr % diameter)) {
			
			compAns = max(compAns, prefix + dfsV[rightPtr]);

			if (prefix <= dfsV[rightPtr]) {
				prefix = dfsV[rightPtr];
			}
			
			prefix += to[cycle[rightPtr]].ss;

			rightPtr = (rightPtr + 1) % diameter;
		}

		cerr << "CompAns = " << compAns << "\n";
		cerr << "-----------------\n";

		ans += compAns;
	}

	cout << ans << "\n";

	return 0;
}

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• Subtask 2: 0 / 3
• Subtask 3: 0 / 4
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