Submission #376927

#	Time	Username	Problem	Language	Result	Execution time	Memory
376927		54skyxenon	Traffic (IOI10_traffic)	C++11	100 / 100	1191 ms	169084 KiB

traffic

#include <iostream>
#include <vector>
#include <numeric>
using namespace std;

#define ll long long

const int maxN = 1e6;

vector<int> adj[maxN];
int congestion[maxN];
int children[maxN];

int total;

// use DP on trees to calculate the max into congestion[curr]
// count number of children ONLY AFTER postorder DFS
void DFS(int P[], int curr, int parent) {
    for (int child : adj[curr]) {
        if (child != parent) {
            DFS(P, child, curr);
            // add all that child branches counts here
            children[curr] += children[child];
            // consider how much congestion total on that child branch
            congestion[curr] = max(congestion[curr], children[child]);
        }
    }

    // count itself in its children value
    children[curr] += P[curr];

    // here, consider if we treated this node as the arena
    // at this point, we've already considered all the children branches while postorder DFS'ing
    // now we consider the congestion of the singular parent branch which was passed over
    congestion[curr] = max(congestion[curr], total - children[curr]);
}

int LocateCentre(int N, int P[], int S[], int D[]) {
    ll minCongestion = 2e9;
    int ans = -1;

    total = accumulate(P, P + N, 0);

    for (int i = 0; i < N - 1; i++) {
       adj[S[i]].push_back(D[i]);
       adj[D[i]].push_back(S[i]);
    }

    // treat the tree rooted at node 0 and DFS
    DFS(P, 0, -1);

    // smooth sailing: just pick the arena with the smallest congestion congestion calculated by DFS
    for (int i = 0; i < N; i++) {
        if (congestion[i] < minCongestion) {
            minCongestion = congestion[i];
            ans = i;
        }
    }

    return ans;
}

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