Submission #125106

#	Time	Username	Problem	Language	Result	Execution time	Memory
125106		NMAC427	Islands (IOI08_islands)	C++17	0 / 100	1137 ms	131072 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.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;
			}
		}
	}


	// Solve
	int ans = 0;

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

		int compAns = 0;

		vector<int> cycle;
		vector<int> dfsV;
		vector<int> 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
		}

		coutV(cycle);


		int tmm = dfsV[0] - prefixSum[0];
		int tp = dfsV[0] + prefixSum[0];

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



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

		// while (leftPtr < diameter && rightPtr < diameter * 2) {

		// 	// cerr << leftPtr << " " << rightPtr << "\n";

		// 	if (leftPtr == (rightPtr % diameter)) {
		// 		prefix -= dfsV[leftPtr];
		// 		prefix -= to[cycle[leftPtr]].ss;
		// 		leftPtr++;
		// 	}

		// 	compAns = max(compAns, prefix + dfsV[rightPtr % diameter]);

		// 	if (prefix <= dfsV[rightPtr % diameter]) {
		// 		prefix  = dfsV[rightPtr % diameter];
		// 		leftPtr = rightPtr % diameter;
		// 	}
			
		// 	prefix   += to[cycle[rightPtr % diameter]].ss;
		// 	rightPtr += 1;
		// }

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

		ans += compAns;
	}

	cout << ans << "\n";

	return 0;
}

Compilation message (stderr)

islands.cpp: In function 'int main()':
islands.cpp:126:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i = 1; i < cycle.size(); i++){
                  ~~^~~~~~~~~~~~~~

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