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Submission #125127

# Submission time Handle Problem Language Result Execution time Memory
125127 2019-07-04T16:31:00 Z NMAC427 Islands (IOI08_islands) C++17
90 / 100
 857 ms 131076 KB 
// 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;
			}
		}
	}

	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;
}

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 376 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 376 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 2 ms 376 KB Output is correct
2 Correct 3 ms 376 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 632 KB Output is correct

Subtask #4
10.0 / 10.0

# Verdict Execution time Memory Grader output
1 Correct 9 ms 1400 KB Output is correct
2 Correct 18 ms 2936 KB Output is correct
3 Correct 12 ms 1784 KB Output is correct
4 Correct 7 ms 1016 KB Output is correct

Subtask #5
10.0 / 10.0

# Verdict Execution time Memory Grader output
1 Correct 25 ms 3620 KB Output is correct
2 Correct 41 ms 6912 KB Output is correct

Subtask #6
10.0 / 10.0

# Verdict Execution time Memory Grader output
1 Correct 92 ms 11180 KB Output is correct
2 Correct 91 ms 18136 KB Output is correct
3 Correct 113 ms 19448 KB Output is correct

Subtask #7
10.0 / 10.0

# Verdict Execution time Memory Grader output
1 Correct 161 ms 22536 KB Output is correct
2 Correct 209 ms 30624 KB Output is correct
3 Correct 216 ms 46440 KB Output is correct
4 Correct 277 ms 45548 KB Output is correct

Subtask #8
10.0 / 10.0

# Verdict Execution time Memory Grader output
1 Correct 341 ms 36548 KB Output is correct
2 Correct 618 ms 60900 KB Output is correct
3 Correct 323 ms 41456 KB Output is correct
4 Correct 415 ms 62768 KB Output is correct
5 Correct 416 ms 60364 KB Output is correct
6 Correct 857 ms 50532 KB Output is correct
7 Correct 432 ms 75576 KB Output is correct

Subtask #9
0 / 10.0

# Verdict Execution time Memory Grader output
1 Runtime error 415 ms 131076 KB Execution killed with signal 9 (could be triggered by violating memory limits)
2 Halted 0 ms 0 KB -