Submission #432824

#	Time	Username	Problem	Language	Result	Execution time	Memory
432824		balbit	Towns (IOI15_towns)	C++14	100 / 100	28 ms	388 KiB

towns

#include "towns.h"

#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define pii pair<int, int>
#define f first
#define s second

#ifdef BALBIT
#define bug(...) cerr<<"#"<<__LINE__<<": "<<#__VA_ARGS__<<"- ", _do(__VA_ARGS__)
template<typename T> void _do( T && x) {cerr<<x<<endl;}
template<typename T, typename ...S> void _do( T && x, S && ...y) {cerr<<x<<", "; _do(y...);}
#else
#define bug(...)
#endif // BALBIT


#define ALL(x) (x).begin(), (x).end()
#define SZ(x) (int )((x).size())
#define pb push_back

#define REP(i,n) for (int i = 0; i<n; ++i)
#define REP1(i,n) for (int i = 1; i<=n; ++i)

#define MX(a,b) a = max(a,b)
#define MN(a,b) a = min(a,b)


map<pii, int> mp;

int getd(int a, int b){
    if (a==b) return 0;
    if (a>b) swap(a,b);
    if (!mp.count({a,b})) mp[{a,b}] = getDistance(a,b);
    return mp[{a,b}];
}

int hubDistance(int n, int sub) {
    mp.clear();
    int p1=-1, p2=-1;
    vector<int> C(n);
    {
        int far = 0;
        REP(i,n) {
            if (i != 0) {
                C[i] = getd(0,i);
                if (getd(0,i) > far) {
                    far = getd(0,i);
                    p1 = i;
                }
            }
        }
    }
    vector<int> A(n);
    vector<int> B(n);
    {
        int far = 0;
        REP(i,n) {
            if (i!=p1) {
                A[i] = getd(p1, i);
                if (getd(p1,i) > far) {
                    far = getd(p1,i);
                    p2 = i;
                }
            }
        }
    }
    assert(p1 != -1 && p2 != -1);
    bug(p1, p2);
    int dia = A[p2];
    int P = (C[p1] + C[p2] - dia) / 2;
    int R = 2000000000;
    bug(P);
    int L = C[p1] - P;
    map<int, vector<pii> > under;
//    int cent = -1;
//    int ncent = -1;
    REP(i,n) {
//        B[i] = getd(p2,i);

        if (A[i] - C[i] == L-P) {
            bug("hI",i);
            under[C[p1] - P].pb({i,A[i] - L});
//            bug(C[i] - P);
            continue;
            // just pretend it's under that
        }
        B[i] = C[p2] + C[i] - P - P;
        int pp = (A[i] + B[i] - dia) / 2;
        bug (i, A[i]-pp, pp);

        under[A[i] - pp].pb({i,pp});
    }
    int who = -1;

    int nstuff = 0;

    for (auto &ele : under) {

        int hi = max(ele.f, dia-ele.f);
//        assert(hi % 2 == 0);
        if (hi < R) {
            R = hi;
            who = -1;
        }
        if (hi == R) {
            if (nstuff <= n/2 && (n - nstuff - SZ(ele.s)) <= n/2) {
//                assert(who == -1);
                who = ele.f;
            }
        }
        nstuff += SZ(ele.s);
    }
    bug(dia, R);
    bug(who);
    for (pii x : under[who]) {
        bug(x.f, x.s);
    }
    if (who == -1) return -R;
    if (SZ(under[who]) <= n/2) return R;
    bug(who);

    vector<pii> fren = under[who];
    {
        vector<vector<int> > dissent;
        vector<int> nfr;
        vector<int> start;
        int hp = 0;
        auto same = [&](int i, int j) {return getd(fren[i].f, fren[j].f) < fren[i].s + fren[j].s;};
        REP(i, SZ(fren)) {
            if (hp == 0) {
                start.pb(i);
                dissent.pb({});
                nfr.pb(1);
                ++hp;
            }else{
                int t = start.back();
                if (same(i, t)) {
                    ++hp; ++nfr.back();
                }else{
                    --hp; dissent.back().pb(i);
                }
            }
        }

        int chk = start.back();
        int num = nfr.back();
        for (int at = SZ(start)-2; at>=0; --at) {
            if (num > n/2) return -R;
            if (same(chk, start[at])) {
                num += nfr[at];
            }else{
                for (int y : dissent[at]) {
                    if (same(chk, y)) {
                        ++num;
                        if (num > n/2) return -R;
                    }
                }
            }
        }
        bug(fren[chk].f, num);
        if (num > n/2) return -R;
    }
    return R;
}

Compilation message (stderr)

towns.cpp: In function 'int hubDistance(int, int)':
towns.cpp:118:14: warning: variable 'x' set but not used [-Wunused-but-set-variable]
  118 |     for (pii x : under[who]) {
      |              ^
towns.cpp:40:28: warning: unused parameter 'sub' [-Wunused-parameter]
   40 | int hubDistance(int n, int sub) {
      |                        ~~~~^~~

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