Submission #1080050

#	Time	Username	Problem	Language	Result	Execution time	Memory
1080050		LittleOrange	Thousands Islands (IOI22_islands)	C++17	10 / 100	127 ms	14292 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);
        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])];
        }
        vector<ll> c(n,0),st;
        function<bool(ll,ll)> dfs;
        dfs = [&](ll i, ll p){
            if (c[i]){
                if (i==0) return true;
                else return false;
            }
            c[i] = 1;
            for(ll j : con[i]) if(v[j]!=p){
                st.push_back(j);
                if(dfs(v[j],i)) return true;
                st.pop_back();
            }
            return false;
        };
        bool ok = dfs(0,-1);
        if(!ok) return false;
        vector<ll> ans;
        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]);
        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: 0 / 21
• Subtask 4: 0 / 24
• Subtask 5: 0 / 45