Submission #1191323

#	Time	Username	Problem	Language	Result	Execution time	Memory
1191323		MatteoArcari	Highway Tolls (IOI18_highway)	C++20	0 / 100	382 ms	327680 KiB

highway

#include <bits/stdc++.h>
using namespace std;
using ll = long long;

ll ask(const vector<int> &w);
void answer(int s, int t);

void find_pair(int n, vector<int> u, vector<int> v, int a, int b) {
    int m = u.size();

    vector<int> w(m, 0);
    ll dst = ask(w) / a;

    vector<vector<int>> adj(n);

    for (int i = 0; i < m; i++) {
        adj[u[i]].push_back(i);
        adj[v[i]].push_back(i);
    }

    int s;

    {
        queue<int> q;
        vector<int> d(n, 1e9), p(n);
        auto dfs = [&](auto &&dfs, int i, int par) -> void {
            if (par != -1) p[i] = par;
            for (int _j: adj[i]) {
                if (_j == par) continue;
                int j = u[_j] ^ v[_j] ^ i;
                dfs(dfs, j, _j);
                d[i] = min(d[i], d[j] + 1);
            }
            if (d[i] == 1e9) {
                d[i] = 0;
            }
        }; dfs(dfs, 0, -1);

        int mid = -1;
        for (int k = 1 << 30; k; k >>= 1) {
            if (mid + k >= d[0]) continue;
            vector<int> ww(m);
            for (int i = 0; i < n; i++) {
                if (d[i] <= mid + k) ww[p[i]] = 1;
            }
            if (ask(ww) == dst) mid += k;
        }
        vector<int> check;
        for (int i = 0; i < n; i++) {
            if (d[i] == mid + 1) check.push_back(i);
        }

        while (check.size() > 1) {
            for (auto &x: w) x = 0;
            for (int i = 0; i < check.size(); i++) {
                if (i & 1) {
                    w[p[check[i]]] = 1;
                }
            }
            vector<int> cc;
            int flag = ask(w) > a * dst;
            for (auto i: check) {
                if (w[p[i]] == flag) {
                    cc.push_back(i);
                }
            }
            check = cc;
        }
        s = check[0];
    }

    vector<int> d(n, -1), check, p(n);
    d[s] = 0;
    queue<int> q; q.push(s);
    while (!q.empty()) {
        int i = q.front();
        q.pop();
        if (d[i] == dst) {
            check.push_back(i);
            continue;
        }
        for (int _j: adj[i]) {
            int j = u[_j] ^ v[_j] ^ i;
            if (d[j] == -1) {
                p[j] = _j;
                d[j] = d[i] + 1;
                q.push(j);
            }
        }
    }

    while (check.size() > 1) {
        for (auto &x: w) x = 0;
        for (int i = 0; i < check.size(); i++) {
            if (i & 1) {
                w[p[check[i]]] = 1;
            }
        }
        vector<int> cc;
        int flag = ask(w) > a * dst;
        for (auto i: check) {
            if (w[p[i]] == flag) {
                cc.push_back(i);
            }
        }
        check = cc;
    }

    answer(s, check[0]);

}

• Subtask 1: 0 / 5
• Subtask 2: 0 / 7
• Subtask 3: 0 / 6
• Subtask 4: 0 / 33
• Subtask 5: 0 / 18
• Subtask 6: 0 / 31