Submission #964021

#	Time	Username	Problem	Language	Result	Execution time	Memory
964021		12345678	City Mapping (NOI18_citymapping)	C++17	100 / 100	12 ms	1116 KiB

citymapping

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

using namespace std;

#define ll long long

mt19937 rng(time(0));

const ll nx=1e3+5;

ll ds[nx];
ll hv[nx], l[nx], sz[nx], rt, pa[nx], w[nx], t;
vector<pair<ll, ll>> k, rnd;
vector<ll> d[nx];
map<pair<ll, ll>, ll> mp;

ll dfssz(ll u)
{
    sz[u]=1;
    for (auto v:d[u]) sz[u]+=dfssz(v);
    if (d[u].size()==1) hv[u]=d[u][0], l[u]=-1;
    else if (d[u].size()==2)
    {
        if (sz[d[u][0]]<sz[d[u][1]]) swap(d[u][0], d[u][1]);
        hv[u]=d[u][0];
        l[u]=d[u][1];
    }  
    return sz[u];
}

ll query(ll u, ll v)
{
    if (u>v) swap(u, v);
    if (mp.find({u, v})!=mp.end()) return mp[{u, v}];
    return mp[{u, v}]=get_distance(u, v);
}

void find_roads(int N, int Q, int A[], int B[], int W[]) {
    pair<ll, ll> mx;
    for (ll i=2; i<=N; i++) rnd.push_back({rng(), i});
    sort(rnd.begin(), rnd.end());
    for (ll i=0; i<min(400, N); i++) mx=max(mx, {query(1, rnd[i].second), rnd[i].second});
    rt=mx.second;
    for (ll i=1; i<=N; i++) if (i!=rt) ds[i]=query(rt, i), k.push_back({ds[i], i});
    sort(k.begin(), k.end());
    for (auto [_, u]:k)
    {
        for (ll i=1; i<=N; i++) hv[i]=l[i]=-1;
        dfssz(rt);
        ll tmp=rt;
        while (1)
        {
            while (hv[tmp]!=-1) tmp=hv[tmp];
            ll ld=query(rt, tmp)-((query(rt, tmp)+query(rt, u))-query(u, tmp))/2;
            while (ld!=0) ld-=w[tmp], tmp=pa[tmp];
            if (d[tmp].size()<2)
            {
                d[tmp].push_back(u), pa[u]=tmp, w[u]=query(u, tmp), A[t]=u, B[t]=tmp, W[t++]=query(u, tmp);
                break;
            }
            else tmp=l[tmp];
        } 
    }
}

• Subtask 1: 9 / 9
• Subtask 2: 16 / 16
• Subtask 3: 13 / 13
• Subtask 4: 19 / 19
• Subtask 5: 43 / 43