Submission #640770

#	Time	Username	Problem	Language	Result	Execution time	Memory
640770		piOOE	Towns (IOI15_towns)	C++17	25 / 100	15 ms	400 KiB

towns

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

using namespace std;

mt19937 rnd(228);

int hubDistance(int n, int sub) {
    map<pair<int, int>, int> mp;
    int limit = (7 * n + 1) / 2;
    auto mygetDistance = [&](int x, int y) {
        if (x == y) {
            mp[{x, x}] = 0;
        }
        if (mp.count({x, y})) {
            return mp[{x, y}];
        } else {
            limit--;
            if (limit < 0) {
                exit(1);
            }
            return mp[{x, y}] = mp[{y, x}] = getDistance(x, y);
        }
    };
    if (sub <= 2) {
        vector<int> dist(n);
        for (int i = 0; i < n; ++i) {
            dist[i] = mygetDistance(i, 0);
        }
        int v = max_element(dist.begin(), dist.end()) - dist.begin();
        for (int i = 0; i < n; ++i) {
            dist[i] = mygetDistance(i, v);
        }
        int u = max_element(dist.begin(), dist.end()) - dist.begin();
        vector<int> dist2(n);
        for (int i = 0; i < n; ++i) {
            dist2[i] = mygetDistance(i, u);
        }
        int ans = numeric_limits<int>::max();
        for (int i = 0; i < n; ++i) {
            int e = dist[i] + dist2[i] - dist[u] >> 1;
            ans = min(ans, max(dist[i] - e, dist2[i] - e));
        }
        return ans;
    } else {
        vector<int> dist0(n), dist(n), e(n);
        for (int i = 0; i < n; ++i) {
            dist0[i] = mygetDistance(i, 0);
        }

        int a = max_element(dist0.begin(), dist0.end()) - dist0.begin();
        for (int i = 0; i < n; ++i) {
            dist[i] = mygetDistance(i, a);
        }

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

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

        vector<int> mega;
        for (int i = 0; i < n; ++i) {
            if (i != b && i != a) {
                e[i] = (dist[i] + dist0[i] - dist[b]) >> 1;
                mega.push_back(dist[i] - e[i]);
                ans = min(ans, max(mega.back(), dist[b] - mega.back()));
            }
        }

        sort(mega.begin(), mega.end());
        mega.resize(unique(mega.begin(), mega.end()) - mega.begin());
        const int m = mega.size();

        vector<int> adj(n), cnt(m);
        vector<vector<int>> kids(m);

        for (int i = 0; i < n; ++i) {
            if (i != b && i != a) {
                adj[i] = lower_bound(mega.begin(), mega.end(), dist[i] - e[i]) - mega.begin();
                kids[adj[i]].push_back(i);
                ++cnt[adj[i]];
            }
        }

        if (sub == 4) {
            for (int i = 0; i < m; ++i) {
                if (max(mega[i], dist[b] - mega[i]) == ans) {
                    int L = 1, R = 1;
                    for (int j = 0; j < i; ++j) {
                        L += cnt[j];
                    }
                    for (int j = i + 1; j < m; ++j) {
                        R += cnt[j];
                    }
                    if (max({L, R, cnt[i]}) <= n / 2) {
                        return ans;
                    }
                }
            }
        } else {
            for (int i = 0; i < m; ++i) {
                if (max(mega[i], dist[b] - mega[i]) == ans) {
                    int now = 0;
                    int L = 1, R = 1;
                    for (int j = 0; j < i; ++j) {
                        L += cnt[j];
                    }
                    for (int j = i + 1; j < m; ++j) {
                        R += cnt[j];
                    }
                    now = max(L, R);
                    if (now > n / 2) {
                        continue;
                    }
                    if (cnt[i] > n / 2) {
                        vector<int> p(n), sz(n, 1);
                        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;
                                sz[x] += sz[y];
                            }
                        };
                        shuffle(kids[i].begin(), kids[i].end(), rnd);
                        int x = kids[i][0], siz = 1;
                        for (int y: kids[i]) {
                            if (y != x && e[x] + e[y] > mygetDistance(x, y)) {
                                ++siz;
                            } else {
                                --siz;
                                if (siz < 0) {
                                    x = y;
                                    siz = 1;
                                }
                            }
                        }
                        if (siz > n / 2) continue;
                        if (cnt[i] / 2 + siz > n / 2) {
                            for (int y: kids[i]) {
                                if (e[x] + e[y] > mygetDistance(x, y)) {
                                    unite(x, y);
                                }
                            }
                            int mx = *max_element(sz.begin(), sz.end());
                            if (mx > n / 2) {
                                continue;
                            }
                        }
                    }
                    return ans;
                }
            }
        }
        return -ans;
    }
}

Compilation message (stderr)

towns.cpp: In function 'int hubDistance(int, int)':
towns.cpp:30:55: warning: conversion from '__gnu_cxx::__normal_iterator<int*, std::vector<int> >::difference_type' {aka 'long int'} to 'int' may change value [-Wconversion]
   30 |         int v = max_element(dist.begin(), dist.end()) - dist.begin();
      |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~
towns.cpp:34:55: warning: conversion from '__gnu_cxx::__normal_iterator<int*, std::vector<int> >::difference_type' {aka 'long int'} to 'int' may change value [-Wconversion]
   34 |         int u = max_element(dist.begin(), dist.end()) - dist.begin();
      |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~
towns.cpp:41:40: warning: suggest parentheses around '-' inside '>>' [-Wparentheses]
   41 |             int e = dist[i] + dist2[i] - dist[u] >> 1;
towns.cpp:51:57: warning: conversion from '__gnu_cxx::__normal_iterator<int*, std::vector<int> >::difference_type' {aka 'long int'} to 'int' may change value [-Wconversion]
   51 |         int a = max_element(dist0.begin(), dist0.end()) - dist0.begin();
      |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~
towns.cpp:56:55: warning: conversion from '__gnu_cxx::__normal_iterator<int*, std::vector<int> >::difference_type' {aka 'long int'} to 'int' may change value [-Wconversion]
   56 |         int b = max_element(dist.begin(), dist.end()) - dist.begin();
      |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~
towns.cpp:71:32: warning: conversion from 'std::vector<int>::size_type' {aka 'long unsigned int'} to 'int' may change value [-Wconversion]
   71 |         const int m = mega.size();
      |                       ~~~~~~~~~^~
towns.cpp:78:80: warning: conversion from '__gnu_cxx::__normal_iterator<int*, std::vector<int> >::difference_type' {aka 'long int'} to '__gnu_cxx::__alloc_traits<std::allocator<int>, int>::value_type' {aka 'int'} may change value [-Wconversion]
   78 |                 adj[i] = lower_bound(mega.begin(), mega.end(), dist[i] - e[i]) - mega.begin();
      |                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~

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