Submission #470076

#	Time	Username	Problem	Language	Result	Execution time	Memory
470076		BlancaHM	Traffic (IOI10_traffic)	C++14	100 / 100	1262 ms	170716 KiB

traffic

#include <iostream>
#include <vector>
using namespace std;
typedef long long int ll;

ll dfs(int S, int parent, vector<vector<int>> & adjList, vector<ll> & DP) {
	for (int v: adjList[S]) {
		if (v == parent)
			continue;
		DP[S] += dfs(v, S, adjList, DP);
	}
	// DP[S] contains the total population in the subtree of S
	return DP[S];
}

int LocateCentre(int N, int P[], int S[], int D[]) {
	vector<ll>DP(N);
	vector<vector<int>> adjList(N, vector<int>());
	for (int i = 0; i < N-1; i++) {
		// we convert the graph format to an adjacency list
		adjList[S[i]].emplace_back(D[i]);
		adjList[D[i]].emplace_back(S[i]);
	}
	for (int i = 0; i < N; i++)
		DP[i] = P[i]; // we initialise the DP so that it contains each city's population

	dfs(0, -1, adjList, DP);

	// we choose 0 originally as our city with lowest maximum congestion and find its largest congestion
	int chosenCity = 0;
	ll chosenCityMaxCongestion = 0;
	for (int rootNeighbour: adjList[0]) {
		chosenCityMaxCongestion = max(chosenCityMaxCongestion, DP[rootNeighbour]);
	}

    // we iterate over all possible chosen cities and compare them with the current record
	for (int currentCity = 1; currentCity < N; currentCity++) {
        // before comparing with the congestion coming from children nodes, we will take as the maximum the congestion travelling from the currentCity's parent to the currentCity
		ll currentCityMaxCongestion = DP[0] - DP[currentCity];

        // we now iterate over the currentCity's children nodes to see if the congestion from a child to the currentCity is higher than that from the parent
		for (int v: adjList[currentCity]) {
			if (DP[v] < DP[currentCity])
				currentCityMaxCongestion = max(currentCityMaxCongestion, DP[v]);
		}

        // if the city's maximum congestion is lower than the current record, we update it
		if (currentCityMaxCongestion < chosenCityMaxCongestion) {
			chosenCityMaxCongestion = currentCityMaxCongestion;
			chosenCity = currentCity;
		}
	}
	return chosenCity;
}

• Subtask 1: 25 / 25
• Subtask 2: 25 / 25
• Subtask 3: 25 / 25
• Subtask 4: 25 / 25