Submission #825480

#	Time	Username	Problem	Language	Result	Execution time	Memory
825480		Liudas	Thousands Islands (IOI22_islands)	C++17	39.40 / 100	1106 ms	707660 KiB

islands

#include "islands.h"
#include <cassert>
#include <fstream>
#include <cstdio>
#include <variant>
#include <vector>
#include <map>
#include <set> 
#include <queue>
#include <unordered_set>
#include <algorithm>
#include <iostream>
using namespace std;
variant<bool, vector<int>> find_journey(int N, int M, vector<int> U, vector<int> V) {
    if (N == 2){
        if(count(U.begin(), U.end(), 0) >= 2 && count(U.begin(), U.end(), 1) >= 1){
            vector<pair<int, int>> ans(M);
            for(int i = 0; i < M; i ++){
                ans[i] = {U[i], i};
            }
            sort(ans.begin(), ans.end());
            vector<int> ret = {ans[0].second, ans.back().second, ans[1].second, ans[0].second, ans.back().second, ans[1].second};
            return ret;
        }
        return false;
    }
    bool N2 = true;
    vector<int> counts(N);
    for(int i = 0; i < M; i ++){
        counts[U[i]]++;
        counts[V[i]]++;
    }
    for(int i = 0; i < N; i ++){
        N2 &= (counts[i] == 2 * N - 2);
    }
    if(N2 && N <= 1000){
        vector<vector<pair<int, int>>> tree(N);
        for(int i = 0; i < M; i ++){
            tree[U[i]].push_back({V[i], i});
        }
        for(int i = 0; i < N; i ++){
            sort(tree[i].begin(), tree[i].end());
        }
        vector<int> ret = {tree[0][0].second, tree[1][0].second, tree[0][1].second, tree[2][0].second, tree[1][0].second, tree[0][0].second, tree[2][0].second, tree[0][1].second};
        return ret;
    }
    bool good = true;
    for(int i = 0; i < M-1; i ++){
        good = V[i] != V[i + 1];
    }
    if(good && N <= 1000){
        vector<vector<pair<int,int>>> tree(N);
        for(int i = 0; i < M; i ++){
            tree[U[i]].push_back({V[i], i});
        }
        vector<int> path;
        int id = 0, par = -1;
        bool back = false;
        int NNN = 0;
        while(tree[id].size() < 3 && tree[id].size() > 0 && !back){
            NNN = max(NNN, (int)tree[id].size());
            if(tree[id].size() == 1){
                par = id;
                path.push_back(tree[id][0].second);
                id = tree[id][0].first;
            }
            else{
                if(tree[id][0].first == par){
                    path.push_back(tree[id][1].second);
                    par = id;
                    id = tree[id][1].first;
                }
                else{
                    path.push_back(tree[id][0].second);
                    par = id;
                    id = tree[id][0].first;
                }
            }
            if(id == 0){
                back = true;
            }
        }
        if(!back && tree[0].size() != 0){
            vector<int> mov, ids;
            for(auto[l, r] : tree[id]){
                if (l != par){
                    mov.push_back(l);
                    ids.push_back(r);
                }
                if(mov.size() > 1){
                    break;
                }
            }
            for(int i = 0; i < M; i ++){
                if(mov[0] == U[i] && id == V[i]){
                    ids.insert(ids.begin() + 1, i);
                    break;
                }
            }
            for(int i = 0; i < M; i ++){
                if(mov[1] == U[i] && id == V[i]){
                    ids.push_back(i);
                    break;
                }
            }
            vector<int> gap;
            if(mov[0] == mov[1]){
                gap = {ids[0], ids[1], ids[2], ids[0], ids[1], ids[2]};
            }
            else{
                gap = {ids[0], ids[1], ids[2], ids[3], ids[1], ids[0], ids[3], ids[2]};
            }
            vector<int> legit;
            for(int i : path){
                legit.push_back(i);
            }
            for(int i : gap){
                legit.push_back(i);
            }
            reverse(path.begin(), path.end());
            for(int i : path){
                legit.push_back(i);
            }
            return legit;
        }
        return false;
    }
    vector<queue<int>> tree(N);
    for(int i = 0; i < M; i ++){
        tree[U[i]].push(V[i]);
    }
    vector<int> path, vis(N, 0);
    path.push_back(0);
    while(path.size()){
        vis[path.back()] = true;
        if(tree[path.back()].size()){
            int a = tree[path.back()].front();
            tree[path.back()].pop();
            path.push_back(a);
            if(vis[path.back()])break;
        }
        else{
            vis[path.back()] = false;
            path.pop_back();
        }
    }
    if(path.size()){
        return path;
    }
    return false;
}

• Subtask 1: 5 / 5
• Subtask 2: 5 / 5
• Subtask 3: 21 / 21
• Subtask 4: 8.399999999999999 / 24
• Subtask 5: 0 / 45