Submission #1080744

#	Time	Username	Problem	Language	Result	Execution time	Memory
1080744		LittleOrange	Thousands Islands (IOI22_islands)	C++17	55 / 100	30 ms	6372 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(m==n*(n-1)){
        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;
        vector<ll> ans;
        if(u[0]!=u[1]){
            vector<ll> st;
            ll cur = 0;
            vector<ll> uu(m,0);
            while(con[cur].size()-(cur!=0)==1){
                for(ll j : con[cur]) if(!uu[j]){
                    uu[j] = 1;
                    uu[inv[j]] = 1;
                    cur = v[j];
                    st.push_back(j);
                    break;
                }
            }
            vector<ll> oks;
                for(ll j : con[cur]) if(!uu[j]&&oks.size()<2){
                    oks.push_back(j);
                }
            if(oks.size()<2) return false;
            for(ll i : st) ans.push_back(i);
            ans.push_back(oks[0]);
            ans.push_back(inv[oks[0]]);
            ans.push_back(oks[1]);
            ans.push_back(inv[oks[1]]);
            ans.push_back(inv[oks[0]]);
            ans.push_back(oks[0]);
            ans.push_back(inv[oks[1]]);
            ans.push_back(oks[1]);
            reverse(st.begin(),st.end());
            for(ll i : st) ans.push_back(i);
        }else{
            //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),uu(n,0);
            ll fr = 0;
            function<bool(ll,ll)> dfs;
            dfs = [&](ll i, ll p){
                if (uu[i]) return false;
                c[i] = 1;
                for(ll j : con[i]) if(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;
                uu[i] = 1;
                return false;
            };
            bool ok = dfs(0,-1);
            if(!ok) return false;
            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);
            for(ll i : st) ans.push_back(inv[i]);
            reverse(st.begin(),st.end());
            for(ll i : st) ans.push_back(i);
            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: 5 / 5
• Subtask 3: 21 / 21
• Subtask 4: 24 / 24
• Subtask 5: 0 / 45