Submission #74209

#	Time	Username	Problem	Language	Result	Execution time	Memory
74209		funcsr	Towns (IOI15_towns)	C++17	35 / 100	35 ms	644 KiB

towns

#include "towns.h"
#include <iostream>
#include <algorithm>
#include <vector>
#include <map>
#include <cassert>
#define rep(i, N) for (int i=0; i<(N); i++)
#define pb push_back
#define _1 first
#define _2 second
#define all(x) x.begin(), x.end()
#define uniq(x) x.erase(unique(all(x)), x.end())
#define INF 1145141919
using namespace std;
typedef pair<int, int> P;
struct UF {
  int U[111];
  int R[111];
  UF(int N) {
    rep(i, N) U[i] = i, R[i] = 1;
  }
  int find(int x) {
    if (U[x]==x)return x;
    return U[x]=find(U[x]);
  }
  void unite(int x, int y) {
    x=find(x), y=find(y);
    if(x==y)return;
    U[y]=x;
    R[x]+=R[y];
    R[y]=0;
  }
};

int N;
int memo[111][111];
int Rank[111];
int dist(int a, int b) {
  if (memo[a][b] != -1) return memo[a][b];
  if (a == b) return 0;
  return memo[a][b] = memo[b][a] = getDistance(a, b);
}
int saien(int x) {
  P mp = P(-1, -1);
  rep(t, N) mp = max(mp, P(dist(x, t), t));
  return mp._2;
}
bool same(int x, int y) {
  if (x==y)return true;
  return dist(x,y)-Rank[x]-Rank[y]!=0;
}

int hubDistance(int NN, int sub) {
  N=NN;
  rep(i, N) rep(j, N) memo[i][j] = -1;
  rep(i, N) Rank[i] = -1;

  int u = saien(0);
  int v = saien(u);
  vector<int> pos;
  int L = dist(u, v);
  pos.pb(0);
  pos.pb(L);
  map<int, vector<int> > G;
  rep(x, N) if (x != u && x != v) {
    Rank[x] = (dist(u, x)+dist(v, x)-L)/2;
    int p = dist(u, x)-Rank[x];
    //cout<<"x="<<x<<"->"<<p<<"\n";
    pos.pb(p);
    G[p].pb(x);
  }
  sort(all(pos)); uniq(pos);
  //cout<<"L="<<L<<"\n";
  //for (int x : pos)cout<<x<<",";cout<<"\n";
  int R = INF;
  for (int x : pos) R = min(R, max(x, L-x));
  vector<int> gs;
  for (int x : pos) if (R == max(x, L-x)) gs.pb(x);
  assert(gs.size()==1||gs.size()==2);

  bool ok = false;
  for (int g : gs) {
    vector<int> list = G[g];
    int left = 1;
    for (int x : pos) if (x<g) left += G[x].size();
    int right = 1;
    for (int x : pos) if (x>g) right += G[x].size();
    int maxsize = max(left, right);
    //cout<<"Left="<<left<<", right="<<right<<"\n";
    assert(left+right+list.size()==N);
    //cout<<"sub="<<sub<<"\n";
    if (maxsize <= N/2 && list.size() > N/2) {
      if (sub == 4) {
        maxsize = max(maxsize, (int)list.size());
      }
      else if (sub >= 3) {
        UF uf(N);
        rep(_, 20) {
          int x = list[rand()%list.size()];
          int ctr = 0;
          for (int y : list) {
            if (uf.find(x) == uf.find(y)) continue;
            if (same(x, y)) {
              ctr++;
              uf.unite(x, y);
            }
            if (ctr > N/2) break;
          }
          maxsize = max(maxsize, ctr);
          if (maxsize > N/2) break;
        }
        /*
        for (int x : list) for (int y :list) if (same(x, y)) uf.unite(x, y);
        for (int x : list) maxsize = max(maxsize, uf.R[uf.find(x)]);
        */
      }
    }
    //cout<<"R="<<R<<", size="<<maxsize<<"\n";
    if (maxsize <= N/2) {
      ok = true;
      break;
    }
  }
  if (!ok) R *= -1;
  return R;
}

Compilation message (stderr)

towns.cpp: In function 'int hubDistance(int, int)':
towns.cpp:85:50: warning: conversion to 'int' from 'std::vector<int>::size_type {aka long unsigned int}' may alter its value [-Wconversion]
     for (int x : pos) if (x<g) left += G[x].size();
                                                  ^
towns.cpp:87:51: warning: conversion to 'int' from 'std::vector<int>::size_type {aka long unsigned int}' may alter its value [-Wconversion]
     for (int x : pos) if (x>g) right += G[x].size();
                                                   ^
In file included from /usr/include/c++/7/cassert:44:0,
                 from towns.cpp:6:
towns.cpp:90:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     assert(left+right+list.size()==N);
            ~~~~~~~~~~~~~~~~~~~~~~^~~
towns.cpp:92:39: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     if (maxsize <= N/2 && list.size() > N/2) {
                           ~~~~~~~~~~~~^~~~~

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