Submission #839856

#	Time	Username	Problem	Language	Result	Execution time	Memory
839856		jtnydv25	Longest Trip (IOI23_longesttrip)	C++17	15 / 100	43 ms	484 KiB

longesttrip

#include "longesttrip.h"

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

#define ll long long
#define all(c) ((c).begin()), ((c).end())
#define sz(x) ((int)(x).size())

#ifdef LOCAL
#include <print.h>
#else
#define trace(...)
#define endl "\n" // remove in interactive
#endif

vector<vector<int>>  remove(vector<vector<int>> P, int a, int b){
    vector<vector<int>> ret;
    for(int i = 0; i < sz(P); i++) if(i != a && i != b) ret.push_back(P[i]);
    return ret;
}

vector<int> longest_trip(int n, int d){
    vector<vector<int>> paths;
    
    vector<int> nodes(n), b(n - 1);
    iota(all(nodes), 0);
    random_shuffle(all(nodes));
    for(int i = 0; i < n - 1; i++){
        b[i] = are_connected({nodes[i]}, {nodes[i + 1]});
    }
    vector<int> vis(n);
    // for(int i = 0; i < n; i++) if(!vis[i]){
    //     int j = i;
    //     vector<int> path;
    //     while(j < n){
    //         path.push_back(nodes[j]);
    //         vis[j] = true;
    //         if(j == n - 1) break;
    //         if(j < n - 1 && b[j]){
    //             j++;
    //             continue;
    //         } else if(j < n - 2 && !b[j + 1]){
    //             j += 2;
    //             continue;
    //         }
    //         break;
    //     }
    //     paths.push_back(path);
    // }
    for(int i = 0; i < n; i++) paths.push_back({i});
    if(sz(paths) == 1) return paths[0];
    // return {};
    while(sz(paths) > 2){
        int k = sz(paths);
        int p = rand() % k, q = rand() % k, r = rand() % k;
        while(p == q || q == r || p == r){
            p = rand() % k, q = rand() % k, r = rand() % k;
        }
        int pp = p, qq = q;
        if(!are_connected({paths[p][0]}, {paths[q][0]})){
            if(rand() % 2) swap(p, q);
            if(are_connected({paths[q][0]}, {paths[r][0]})){
                pp = q; qq = r;
            } else{
                // qq = r;
                pp = p; qq = r;
            }
        }
        vector<int> newpath = paths[pp];
        reverse(all(newpath));
        copy(all(paths[qq]), back_inserter(newpath));
        paths = remove(paths, pp, qq);
        paths.push_back(newpath);
    }

    for(int i = 0; i < 2; i++){
        for(int j = 0; j < 2; j++){
            if(are_connected({paths[0][0]}, {paths[1][0]})){
                vector<int> Q = paths[0];
                reverse(all(Q));
                copy(all(paths[1]), back_inserter(Q));
                return Q;
            }
            reverse(all(paths[1]));
        }
        reverse(all(paths[0]));
    }

    vector<int> P = paths[0], Q = paths[1];
    if(are_connected(paths[0], paths[1])){
        for(int i = 0; i < 2; i++){
            while(sz(paths[i]) > 1){
                int k = sz(paths[i]) / 2;
                vector<int> lft(paths[i].begin(), paths[i].begin() + k);
                vector<int> rgt(paths[i].begin() + k, paths[i].end());
                if(are_connected(lft, paths[i ^ 1])){
                    paths[i] = lft;
                } else paths[i] = rgt;
            }
        }
        vector<int> final_path;
        int posP = find(all(P), paths[0][0]) - P.begin();
        int posQ = find(all(P), paths[0][0]) - P.begin();
        posP = (posP + 1) % sz(P);
        rotate(P.begin(), P.begin() + posP, P.end());
        rotate(Q.begin(), Q.begin() + posQ, Q.end());
        copy(all(Q), back_inserter(P));
        return P;
    }

    return sz(paths[0]) > sz(paths[1]) ? paths[0] : paths[1];
}

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