Submission #640797

#	Time	Username	Problem	Language	Result	Execution time	Memory
640797		piOOE	Towns (IOI15_towns)	C++17	25 / 100	21 ms	364 KiB

towns

#include <bits/stdc++.h>
#include "towns.h"

using namespace std;

int hubDistance(int n, int sub) {
    vector<int> dist0(n);
    for (int i = 1; i < n; ++i) {
        dist0[i] = getDistance(0, i);
    }

    int a = max_element(dist0.begin(), dist0.end()) - dist0.begin();

    vector<int> dist(n);
    dist[0] = dist0[a];
    for (int i = 1; i < n; ++i) {
        dist[i] = i == a ? 0 : getDistance(i, a);
    }

    int b = max_element(dist.begin(), dist.end()) - dist.begin();

    vector<int> pos(n);
    pos[0] = (dist0[a] - dist0[b] + dist[b]) >> 1;
    for (int i = 1; i < n; ++i) {
        pos[i] = min(pos[0], (dist0[a] - dist0[i] + dist[i]) >> 1);
    }

    int ans = numeric_limits<int>::max();

    map<int, vector<int>> mp;

    for (int i = 0; i < n; ++i) {
        ans = min(ans, max(pos[i], dist[b] - pos[i]));
        mp[pos[i]].push_back(i);
    }

    int L = 0, R = n;
    for (auto [len, adj]: mp) {
        R -= adj.size();

        if (max(len, dist[b] - len) == ans && max(L, R) <= n / 2) {
            if (adj.size() <= n / 2) {
                return ans;
            }
            vector<int> p(n);
            iota(p.begin(), p.end(), 0);
            auto get = [&](int x) {
                while (x != p[x]) x = p[x] = p[p[x]];
                return x;
            };
            auto unite = [&](int x, int y) {
                x = get(x), y = get(y);
                if (x != y) {
                    p[y] = x;
                }
            };

            auto same = [&](int x, int y) {
                return get(x) == get(y);
            };

            int x = adj[0], siz = 1;
            vector<int> S, T;
            for (int y: adj) {
                if (x != y) {
                    if (dist[x] + dist[y] - 2 * len > getDistance(x, y)) {
                        unite(x, y);
                        S.push_back(y);
                    } else {
                        T.push_back(y);
                        if (T.size() > S.size()) {
                            x = y;
                            swap(S, T);
                        }
                    }
                }
            }
            int sz = 0;
            for (int y : S) {
                if (same(x, y) || dist[x] + dist[y] - 2 * len > getDistance(x, y)) {
                    unite(x, y);
                    ++sz;
                }
            }
            if (sz * 2 <= n) {
                return ans;
            } else {
                return -ans;
            }
        }
        L += adj.size();
    }

    return -ans;
}

Compilation message (stderr)

towns.cpp: In function 'int hubDistance(int, int)':
towns.cpp:12:53: warning: conversion from '__gnu_cxx::__normal_iterator<int*, std::vector<int> >::difference_type' {aka 'long int'} to 'int' may change value [-Wconversion]
   12 |     int a = max_element(dist0.begin(), dist0.end()) - dist0.begin();
      |             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~
towns.cpp:20:51: warning: conversion from '__gnu_cxx::__normal_iterator<int*, std::vector<int> >::difference_type' {aka 'long int'} to 'int' may change value [-Wconversion]
   20 |     int b = max_element(dist.begin(), dist.end()) - dist.begin();
      |             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~
towns.cpp:39:23: warning: conversion from 'std::vector<int>::size_type' {aka 'long unsigned int'} to 'int' may change value [-Wconversion]
   39 |         R -= adj.size();
      |                       ^
towns.cpp:42:28: warning: comparison of integer expressions of different signedness: 'std::vector<int>::size_type' {aka 'long unsigned int'} and 'int' [-Wsign-compare]
   42 |             if (adj.size() <= n / 2) {
      |                 ~~~~~~~~~~~^~~~~~~~
towns.cpp:62:29: warning: unused variable 'siz' [-Wunused-variable]
   62 |             int x = adj[0], siz = 1;
      |                             ^~~
towns.cpp:91:23: warning: conversion from 'std::vector<int>::size_type' {aka 'long unsigned int'} to 'int' may change value [-Wconversion]
   91 |         L += adj.size();
      |                       ^
towns.cpp:6:28: warning: unused parameter 'sub' [-Wunused-parameter]
    6 | int hubDistance(int n, int sub) {
      |                        ~~~~^~~

• Subtask 1: 13 / 13
• Subtask 2: 12 / 12
• Subtask 3: 0 / 13
• Subtask 4: 0 / 10
• Subtask 5: 0 / 13
• Subtask 6: 0 / 39