Submission #410097

#	Time	Username	Problem	Language	Result	Execution time	Memory
410097		definitelynotmee	Towns (IOI15_towns)	C++98	100 / 100	23 ms	856 KiB

towns

// Que problema lindo. Muito foda jeito e o motivo que tudo só se encaixa na solução pra 100 pontos
#include <bits/stdc++.h>
#include "towns.h"
#define mp make_pair
#define mt make_tuple
#define ff first
#define ss second
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
const ll INFL = (1LL<<62)-1;
const int INF = (1<<30)-1;
const int MAXN = 0;

int getDistance(int i, int j);

inline bool check(int i, int j, vector<bool>& v, vector<int>& db, int lb, int a){

    if(i==j)
        return 1;
    if(v[i]^v[j])
        return 0;
    if(v[i])
        return 1;
    
    int L = (db[i] + db[j] - getDistance(i,j))>>1;
    return min(L,db[a]-L) != lb;
}

int hubDistance(int n, int sub){
    int a = 0, b;
    vector<int> ds (n,0), db(n,0);

    int maxi = -1;
    for(int i = 1; i < n; i++){
        ds[i] = getDistance(0,i);
        if(ds[i] > maxi)
            maxi = ds[i], b = i;
    }
    maxi = ds[b];
    db[0] = ds[b];
    for(int i = 1; i < n; i++){
        if(i==b)
            continue;
        db[i] = getDistance(b,i);
        if(db[i] > maxi)
            maxi = db[i], a = i;
    }
    vector<int> dlca(n,0); // dist(lca(x,0) na arvore enraizada no b, b)
    vector<bool> bsub(n,0); // verdadeiro se x está na subarvore do b
    int resp = INF;
    for(int i = 0; i < n; i++){
        dlca[i] = (db[0] + db[i] - ds[i])>>1;
        resp = min(resp, max(dlca[i], db[a] - dlca[i]));
    }
    int lb = min(resp, db[a]-resp);
    for(int i = 0; i < n; i++){
        if(dlca[i] < lb)
            bsub[i] = 1;
    }

    // ao parear os indices e considerar apenas aqueles que estão no mesmo grupo,
    // caso haja um majoritário ele será majoritário tanto no vetor inicial quanto no modificado

    stack<int,vector<int>> st;
    vector<bool> par(n,0); // verdadeiro se x estiver pareado
    for(int i = 0; i < (n>>1); i++){
        int cur = 2*i;
        //cout << "check(" << cur << "," << cur+1 << ") = " << check(cur,cur+1,bsub,db, lb,a) << '\n';
        if(!check(cur,cur+1,bsub,db, lb,a))
            continue;
        par[cur] = 1;
        par[cur+1] = 1;
        if(st.empty()){
            st.push(cur);
        } else {
            //cout << "check(" << st.top() << "," << cur << ") = " << check(st.top(), cur, bsub,db,lb,a) << '\n';
            if(check(st.top(), cur, bsub,db,lb,a))
                st.push(cur);
            else st.pop();
        }
    }
    int major = (st.empty() ? n-1 : st.top());
    //cout << "pares ->";
    //for(bool i : par)
    //    cout << i;
    //cout << '\n';
    int majorcount = 0;
    for(int i = 0; i < n; i++){
        if(par[i]){
            if(i&1)
                continue;
            //cout << "check(" << i << "," << major << ") = " << check(i,major,bsub,db,lb,a) << '\n';
            if(check(i,major,bsub,db,lb,a))
                majorcount+=2;
        } else {
            //cout << "check(" << i << "," << major << ") = " << check(i,major,bsub,db,lb,a) << '\n';
            if(check(i,major,bsub,db,lb,a))
                majorcount++;
        }
        
    }
    //cout << major << ' ' << majorcount << "\n";
    if(majorcount > (n>>1))
        resp*=-1;
    return resp;
}

Compilation message (stderr)

towns.cpp: In function 'int hubDistance(int, int)':
towns.cpp:31:28: warning: unused parameter 'sub' [-Wunused-parameter]
   31 | int hubDistance(int n, int sub){
      |                        ~~~~^~~
towns.cpp:41:16: warning: 'b' may be used uninitialized in this function [-Wmaybe-uninitialized]
   41 |     maxi = ds[b];
      |                ^

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