Submission #1080090

#	Time	Username	Problem	Language	Result	Execution time	Memory
1080090		LittleOrange	Thousands Islands (IOI22_islands)	C++17	6.75 / 100	1077 ms	4976 KiB

islands

#include "islands.h"

#include <variant>
#include <vector>
#include <bits/stdc++.h>
using namespace std;
using ll = int;

std::variant<bool, std::vector<int>> find_journey(
    int n, int m, std::vector<int> u, std::vector<int> v){
    if (n == 2){
        vector<ll> a,b;
        for(ll i = 0;i<m;i++){
            if (u[i]==0) a.push_back(i);
            else b.push_back(i);
        }
        if (a.size()<2||b.size()<1) return false;
        return vector<ll>({a[0],b[0],a[1],a[0],b[0],a[1]});
    }
    if(0){
        vector<ll> a(6);
        for(ll i = 0;i<m;i++){
            if (u[i]==0&&v[i]==1) a[0] = i;
            if (u[i]==1&&v[i]==2) a[1] = i;
            if (u[i]==2&&v[i]==0) a[2] = i;
            if (u[i]==0&&v[i]==2) a[3] = i;
            if (u[i]==2&&v[i]==1) a[4] = i;
            if (u[i]==1&&v[i]==0) a[5] = i;
        }
        return vector<ll>({a[0],a[1],a[2],a[3],a[4],a[5],a[2],a[1],a[0],a[5],a[4],a[3]});
    }
    if(m%2==0){
        vector<vector<ll>> con(n);
        for(ll i = 0;i<m;i++){
            con[u[i]].push_back(i);
        }
        vector<ll> inv(m);
        for(ll i = 0;i<m;i++) inv[i] = i^1;
        //map<pair<ll,ll>,ll> mp;
        //for(ll i = 0;i<m;i++){
        //    mp[make_pair(u[i],v[i])] = i;
        //}
        //for(ll i = 0;i<m;i++){
        //    inv[i] = mp[make_pair(v[i],u[i])];
        //}
        deque<ll> c(n,0),st,ins(m,0);
        ll fr = 0;
        function<bool(ll,ll)> dfs;
        dfs = [&](ll i, ll p){
            c[i] = 1;
            for(ll j : con[i]) if(!ins[j]&&inv[j]!=p){
                st.push_back(j);
                ins[j] = 1;
                if (c[v[j]]){
                    fr = v[j];
                    return true;
                }
                if(dfs(v[j],j)) return true;
                ins[j] = 0;
                st.pop_back();
            }
            c[i] = 0;
            return false;
        };
        bool ok = dfs(0,-1);
        if(!ok) return true;
        vector<ll> ans;
        vector<ll> beg;
        while(u[st.front()]!=fr){
            beg.push_back(st.front());
            st.pop_front();
        }
        for(ll i : beg) ans.push_back(i);
        for(ll i : st) ans.push_back(i);
        reverse(st.begin(),st.end());
        for(ll i : st) ans.push_back(inv[i]);
        for(ll i : st) ans.push_back(i);
        reverse(st.begin(),st.end());
        for(ll i : st) ans.push_back(inv[i]);
        reverse(beg.begin(),beg.end());
        for(ll i : beg) ans.push_back(i);
        return ans;
    }
    if (n == 4){
        return std::vector<int>({0, 1, 2, 4, 0, 3, 2, 1, 4, 3});
    }
    return false;
}

• Subtask 1: 5 / 5
• Subtask 2: 1.75 / 5
• Subtask 3: 0 / 21
• Subtask 4: 0 / 24
• Subtask 5: 0 / 45