Submission #824280

#	Time	Username	Problem	Language	Result	Execution time	Memory
824280		Liudas	Thousands Islands (IOI22_islands)	C++17	10 / 100	249 ms	5464 KiB

islands

#include "islands.h"
#include <cassert>
#include <cstdio>
#include <variant>
#include <vector>
#include <algorithm>
#include <iostream>
using namespace std;
bool loop = false;
void dfs(int node, vector<vector<pair<int, int>>> &tree, vector<bool> &vis){
    if(vis[node]){
        loop = true;
        return;
    }
    vis[node] = true;
    for(auto&[l, r] : tree[node]){
        if(!r){
            r = true;
            dfs(l, tree, vis);
        }
    }
    vis[node] = false;
}
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;
    for(int i = 0; i < N; i ++){
        N2 &= ((count(U.begin(), U.end(), i) + count(V.begin(), V.end(), i)) == 2 * N - 2);
    }
    if(N2){
        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;
    }
    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;
    }
    tree.clear();
    tree.assign(N, {});
    for(int i = 0; i < M; i ++){
        tree[U[i]].push_back({V[i], 0});
    }
    vector<bool> vis(N, 0);
    dfs(0, tree, vis);
    vector<int> arr(3, 0);
    if(loop){
        return arr;
    }
    return false;
}

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