Submission #628554

#	Time	Username	Problem	Language	Result	Execution time	Memory
628554		Sorting	Thousands Islands (IOI22_islands)	C++17	31 / 100	46 ms	5152 KiB

islands

#include "islands.h"

#include <variant>
#include <vector>
#include <algorithm>
#include <cmath>

using namespace std;

std::variant<bool, std::vector<int>> find_journey(
    int n, int m, std::vector<int> u, std::vector<int> v) {
    if(n == 2){
        vector<int> cnt[2]{};
        for(int i = 0; i < u.size();++i){
            cnt[u[i]].push_back(i);
        }
        
        if(cnt[0].size() >= 2 && cnt[1].size() >= 1){
            return vector<int>{cnt[0][0], cnt[1][0], cnt[0][1], cnt[0][0], cnt[1][0], cnt[0][1]};
        }
        return false;
    }
    vector<vector<pair<int, int>>> adj(n);
    for(int i = 0; i < m; ++i)
        adj[u[i]].push_back({v[i], i});

    vector<int> ans;
    
    int x = 0, par = -1;
    while(true){
        if(adj[x].size() != 1 + (x != 0)){
            if(adj[x].size() < 1 + (x != 0)){
                return false;
            }
            int len = ans.size();
            pair<int, int> to_1{-1, -1}, to_2{-1, -1};
            for(auto p: adj[x]){
                if(p.first == par){
                    continue;
                }
                if(to_1.first == -1)
                    to_1 = p;
                else
                    to_2 = p;
            }

            if(to_1.first == to_2.first){
                pair<int, int> back_1{-1, -1}, back_2{-1, -1};
                for(auto p: adj[to_1.first]){
                    if(p.first != x){
                        continue;
                    }
                    if(back_1.first == -1)
                        back_1 = p;
                    else
                        back_2 = p;
                }

                ans.push_back(to_1.second);
                ans.push_back(back_1.second);
                ans.push_back(to_2.second);
                ans.push_back(to_1.second);
                ans.push_back(back_1.second);
                ans.push_back(to_2.second);
            }
            else{
                pair<int, int> back_1{-1, -1}, back_2{-1, -1};
                for(auto p: adj[to_1.first]){
                    if(p.first != x)
                        continue;
                    back_1 = p;
                    break;
                }
                for(auto p: adj[to_2.first]){
                    if(p.first != x)
                        continue;
                    back_2 = p;
                    break;
                }

                ans.push_back(to_1.second);
                ans.push_back(back_1.second);
                ans.push_back(to_2.second);
                ans.push_back(back_2.second);
                ans.push_back(back_1.second);
                ans.push_back(to_1.second);
                ans.push_back(back_2.second);
                ans.push_back(to_2.second);
            }

            for(int i = len - 1; i >= 0; --i)
                ans.push_back(ans[i]);

            return ans;
        }
        for(auto p: adj[x]){
            int to = p.first;
            int idx = p.second;
            if(to == par){
                par = -1;
                continue;
            }
            par = x;
            x = to;
            ans.push_back(idx);
            break;
        }
    }
}

Compilation message (stderr)

islands.cpp: In function 'std::variant<bool, std::vector<int, std::allocator<int> > > find_journey(int, int, std::vector<int>, std::vector<int>)':
islands.cpp:14:26: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   14 |         for(int i = 0; i < u.size();++i){
      |                        ~~^~~~~~~~~~

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