Submission #840681

#	Time	Username	Problem	Language	Result	Execution time	Memory
840681		Lucpp	Longest Trip (IOI23_longesttrip)	C++17	100 / 100	20 ms	432 KiB

longesttrip

#include <bits/stdc++.h>
#include "longesttrip.h"
using namespace std;
#define sz(x) (int)(x.size())

mt19937 rng(42);

map<pair<int, int>, bool> cache;

bool qry(int a, int b){
    if(a > b) swap(a, b);
    auto p = make_pair(a, b);
    if(cache.count(p)) return cache[p];
    else return cache[p] = are_connected({a}, {b});
}

vector<int> longest_trip(int N, int D){
    cache.clear();
    (void)D;
    vector<int> ord(N);
    for(int i = 0; i < N; i++) ord[i] = i;
    shuffle(ord.begin(), ord.end(), rng);
    vector<vector<int>> paths{{ord[0]}, {ord[1]}};
    for(int k = 2; k < N; k++){
        int i = ord[k];
        int j = rng() % 2;
        if(rng() % 2){
            if(qry(paths[0].back(), paths[1].back())){
                paths[0].insert(paths[0].end(), paths[1].rbegin(), paths[1].rend());
                paths[1] = {i};
            }
            else if(qry(paths[j].back(), i)) paths[j].push_back(i);
            else paths[j^1].push_back(i);
        }
        else{
            if(qry(paths[j].back(), i)) paths[j].push_back(i);
            else if(qry(paths[0].back(), paths[1].back())){
                paths[0].insert(paths[0].end(), paths[1].rbegin(), paths[1].rend());
                paths[1] = {i};
            }
            else paths[j^1].push_back(i);
        }
    }
    if(!are_connected(paths[0], paths[1])){
        return sz(paths[0]) > sz(paths[1]) ? paths[0] : paths[1];
    }
    for(int i = 0; i < 2; i++){
        if(sz(paths[i]) < 3) continue;
        if(!qry(paths[i][0], paths[i].back())){
            if(are_connected({paths[i][0]}, {paths[i^1][0]})){
                reverse(paths[i].begin(), paths[i].end());
            }
            paths[i].insert(paths[i].end(), paths[i^1].begin(), paths[i^1].end());
            return paths[i];
        }
    }
    auto prefix = [&](vector<int> v, int len){
        vector<int> w;
        for(int i = 0; i <= len; i++) w.push_back(v[i]);
        return w;
    };
    int lo = 0, hi = sz(paths[0])-1;
    while(lo < hi){
        int m = (lo+hi)/2;
        if(are_connected(prefix(paths[0], m), paths[1])) hi = m;
        else lo = m+1;
    }
    int p1 = lo;
    lo = 0, hi = sz(paths[1])-1;
    while(lo < hi){
        int m = (lo+hi)/2;
        if(are_connected(prefix(paths[0], p1), prefix(paths[1], m))) hi = m;
        else lo = m+1;
    }
    vector<int> res;
    for(int i = 1; i <= sz(paths[0]); i++){
        res.push_back(paths[0][(p1+i)%sz(paths[0])]);
    }
    for(int i = 0; i < sz(paths[1]); i++){
        res.push_back(paths[1][(lo+i)%sz(paths[1])]);
    }
    return res;
}

• Subtask 0: 0 / 0
• Subtask 1: 5 / 5
• Subtask 2: 10 / 10
• Subtask 3: 25 / 25
• Subtask 4: 60 / 60