Submission #794069

#	Time	Username	Problem	Language	Result	Execution time	Memory
794069		PixelCat	Towns (IOI15_towns)	C++14	39 / 100	17 ms	916 KiB

towns

#ifdef NYAOWO
#include "grader.cpp"
#endif

#include "towns.h"

#include <bits/stdc++.h>
#define For(i, a, b) for(int i = a; i <= b; i++)
#define Forr(i, a, b) for(int i = a; i >= b; i--)
#define F first
#define S second
#define all(x) x.begin(), x.end()
#define sz(x) ((int)x.size())
#define eb emplace_back
#define int LL
using namespace std;
using LL = long long;
using pii = pair<int, int>;

mt19937_64 rng(1011101148763ll);

map<pii, int> mem;
int dist(int a, int b) {
    if(a > b) swap(a, b);
    pii p(a, b);
    if(mem.count(p)) return mem[p];
    mem[p] = getDistance((int32_t)a, (int32_t)b);
    return mem[p];
}

int32_t hubDistance(int32_t N, int32_t sub) {
    // remember to init!
    mem.clear();

    vector<int> al(N);
    For(i, 0, N - 1) al[i] = i;

    int dia = 0;
    int p1 = 0;
    shuffle(all(al), rng);
    for(auto &i:al) {
        int d = dist(i, 0);
        if(d > dia) {
            dia = d;
            p1 = i;
        }
    }
    dia = 0;
    int p2 = p1;
    shuffle(all(al), rng);
    for(auto &i:al) {
        int d = dist(p1, i);
        if(d > dia) {
            dia = d;
            p2 = i;
        }
    }

    map<int, int> cnt;
    map<int, vector<int>> child;
    For(i, 0, N - 1) if(i != p1 && i != p2) {
        int d1 = dist(p1, i);
        int d2 = dist(p2, i);
        int d = (dia + d1 - d2) / 2;
        cnt[d]++;
        child[d].eb(i);
    }

    auto check = [&](int d, vector<int> v) {
        int jury = 0;
        int hp = 0;
        for(auto &i:v) {
            if(hp == 0) {
                jury = i; hp = 1;
            } else if(d * 2 < dist(p1, jury) + dist(p1, i) - dist(jury, i)) {
                hp++;
            } else {
                hp--;
            }
        }
        hp = 0;
        for(auto &i:v) {
            if(d * 2 < dist(p1, jury) + dist(p1, i) - dist(jury, i)) {
                hp++;
            }
        }
        return hp * 2 <= N;
    };
    
    int mn = dia;
    vector<int> pos, val;
    vector<int> pre, suf;
    for(auto &i:cnt) {
        mn = min(mn, max(i.F, dia - i.F));
        pos.eb(i.F);
        val.eb(i.S);
        pre.eb(0);
        suf.eb(0);
    }
    int m = sz(pos);
    pre[0] = 1;
    For(i, 1, m - 1) pre[i] = pre[i - 1] + val[i - 1];
    suf[m - 1] = 1;
    Forr(i, m - 2, 0) suf[i] = suf[i + 1] + val[i + 1];
    bool balanced = false;
    For(i, 0, m - 1) {
        if(max(pos[i], dia - pos[i]) == mn) {
            int mx_sub = max({val[i], pre[i], suf[i]});
            if(2 * mx_sub <= N) balanced = true;
        }
    }
    if(!balanced) For(i, 0, m - 1) {
        if(max(pos[i], dia - pos[i]) == mn) {
            if(val[i] * 2 > N && check(pos[i], child[pos[i]])) balanced = true;
        }
    }
    if(!balanced) mn = -mn;
    return (int32_t)mn;
}

Compilation message (stderr)

towns.cpp: In function 'int32_t hubDistance(int32_t, int32_t)':
towns.cpp:31:40: warning: unused parameter 'sub' [-Wunused-parameter]
   31 | int32_t hubDistance(int32_t N, int32_t sub) {
      |                                ~~~~~~~~^~~

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