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Submission #125119

# Submission time Handle Problem Language Result Execution time Memory
125119 2019-07-04T16:17:42 Z NMAC427 Islands (IOI08_islands) C++17
90 / 100
 1028 ms 131072 KB 
// https://oj.uz/problem/view/IOI08_islands

#include <bits/stdc++.h>
#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
		}


		int prefixFwd = dfsV[0];
		int 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;
}

Compilation message

islands.cpp: In function 'int main()':
islands.cpp:123:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i = 1; i < cycle.size(); i++) {
                  ~~^~~~~~~~~~~~~~

Subtask #1
33.0 / 33.0

# Verdict Execution time Memory Grader output
1 Correct 2 ms 376 KB Output is correct
2 Correct 2 ms 380 KB Output is correct
3 Correct 2 ms 376 KB Output is correct
4 Correct 2 ms 376 KB Output is correct
5 Correct 2 ms 376 KB Output is correct
6 Correct 2 ms 376 KB Output is correct
7 Correct 2 ms 376 KB Output is correct
8 Correct 2 ms 376 KB Output is correct
9 Correct 2 ms 376 KB Output is correct
10 Correct 2 ms 248 KB Output is correct
11 Correct 2 ms 376 KB Output is correct

Subtask #2
3.0 / 3.0

# Verdict Execution time Memory Grader output
1 Correct 3 ms 384 KB Output is correct
2 Correct 3 ms 504 KB Output is correct

Subtask #3
4.0 / 4.0

# Verdict Execution time Memory Grader output
1 Correct 3 ms 504 KB Output is correct
2 Correct 4 ms 732 KB Output is correct

Subtask #4
10.0 / 10.0

# Verdict Execution time Memory Grader output
1 Correct 10 ms 1528 KB Output is correct
2 Correct 20 ms 3200 KB Output is correct
3 Correct 12 ms 1912 KB Output is correct
4 Correct 7 ms 1116 KB Output is correct

Subtask #5
10.0 / 10.0

# Verdict Execution time Memory Grader output
1 Correct 26 ms 4652 KB Output is correct
2 Correct 42 ms 8536 KB Output is correct

Subtask #6
10.0 / 10.0

# Verdict Execution time Memory Grader output
1 Correct 92 ms 14380 KB Output is correct
2 Correct 95 ms 20564 KB Output is correct
3 Correct 117 ms 22096 KB Output is correct

Subtask #7
10.0 / 10.0

# Verdict Execution time Memory Grader output
1 Correct 165 ms 26428 KB Output is correct
2 Correct 212 ms 41440 KB Output is correct
3 Correct 225 ms 56072 KB Output is correct
4 Correct 281 ms 61376 KB Output is correct

Subtask #8
10.0 / 10.0

# Verdict Execution time Memory Grader output
1 Correct 355 ms 49492 KB Output is correct
2 Correct 663 ms 77024 KB Output is correct
3 Correct 337 ms 58872 KB Output is correct
4 Correct 423 ms 84384 KB Output is correct
5 Correct 434 ms 81964 KB Output is correct
6 Correct 1028 ms 73792 KB Output is correct
7 Correct 443 ms 98848 KB Output is correct

Subtask #9
0 / 10.0

# Verdict Execution time Memory Grader output
1 Runtime error 428 ms 131072 KB Execution killed with signal 9 (could be triggered by violating memory limits)
2 Halted 0 ms 0 KB -