Submission #1010863

#	Time	Username	Problem	Language	Result	Execution time	Memory
1010863		GrindMachine	Thousands Islands (IOI22_islands)	C++17	55 / 100	36 ms	10836 KiB

islands

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace std;
using namespace __gnu_pbds;

template<typename T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
typedef long long int ll;
typedef long double ld;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;

#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL)
#define pb push_back
#define endl '\n'
#define sz(a) (int)a.size()
#define setbits(x) __builtin_popcountll(x)
#define ff first
#define ss second
#define conts continue
#define ceil2(x,y) ((x+y-1)/(y))
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define yes cout << "Yes" << endl
#define no cout << "No" << endl

#define rep(i,n) for(int i = 0; i < n; ++i)
#define rep1(i,n) for(int i = 1; i <= n; ++i)
#define rev(i,s,e) for(int i = s; i >= e; --i)
#define trav(i,a) for(auto &i : a)

template<typename T>
void amin(T &a, T b) {
    a = min(a,b);
}

template<typename T>
void amax(T &a, T b) {
    a = max(a,b);
}

#ifdef LOCAL
#include "debug.h"
#else
#define debug(...) 42
#endif

/*



*/

const int MOD = 1e9 + 7;
const int N = 1e5 + 5;
const int inf1 = int(1e9) + 5;
const ll inf2 = ll(1e18) + 5;

#include "islands.h"

vector<pii> adj[N];
vector<bool> vis(N), recstack(N);
vector<pii> par(N,{-1,-1});
bool cyc = false;
vector<int> ans;

void dfs1(int u){
    vis[u] = 1;
    recstack[u] = 1;

    for(auto [v,id] : adj[u]){
        if(vis[v]){
            if(recstack[v]){
                if(!cyc){
                    cyc = true;
                    int curr = u;
                    vector<int> cyc_edges;
                    while(curr != v){
                        cyc_edges.pb(par[curr].ss);
                        curr = par[curr].ff;
                    }
                    reverse(all(cyc_edges));
                    cyc_edges.pb(id);
                    vector<int> par_edges;
                    curr = v;
                    while(curr){
                        par_edges.pb(par[curr].ss);
                        curr = par[curr].ff;
                    }

                    ans = par_edges;

                    reverse(all(ans));

                    trav(x,cyc_edges) ans.pb(x);
                    ans.pb(cyc_edges[0]^1);
                    ans.pb(cyc_edges[0]);
                    rev(i,sz(cyc_edges)-1,1){
                        ans.pb(cyc_edges[i]);
                    }
                    ans.pb(cyc_edges[0]^1);

                    trav(x,par_edges) ans.pb(x);
                }
            }
        }
        else{
            par[v] = {u,id};
            dfs1(v);
        }
    }

    recstack[u] = 0;
}

bool line = true;
vector<bool> good(N);

void dfs2(int u, int p){
    vis[u] = 1;
    int d = sz(adj[u])-(p != -1);
    if(d >= 2){
        good[u] = 1;
        line = false;
    }

    for(auto [v,id] : adj[u]){
        if(v == p or vis[v]) conts;
        par[v] = {u,id};
        dfs2(v,u);
    }
}

std::variant<bool, std::vector<int>> find_journey(
    int n, int m, std::vector<int> U, std::vector<int> V) {

    rep(i,m){
        int u = U[i], v = V[i];
        adj[u].pb({v,i});
    }

    if(n == 2){
        if(!(sz(adj[0]) >= 2 and sz(adj[1]) >= 1)){
            return false;
        }

        int x = adj[0][0].ss, y = adj[0][1].ss, z = adj[1][0].ss;
        vector<int> ans = {x,z,y,x,z,y};
        return ans;
    }

    bool subtask4 = true, subtask3 = true;
    rep(i,m){
        if(!(m&1)){
            if(U[i] == U[i^1] and V[i] == V[i^1]){

            }
            else{
                subtask4 = false;
            }

            swap(U[i],V[i]);

            if(U[i] == U[i^1] and V[i] == V[i^1]){

            }
            else{
                subtask3 = false;
            }

            swap(U[i],V[i]);
        }
    }

    if(subtask4){
        dfs1(0);
        if(cyc) return ans;
        else return false;
    }

    if(subtask3){
        dfs2(0,-1);
        if(line){
            return false;
        }
     
        rep(i,n){
            if(!good[i]) conts;
            bool ok = true;
            int u = i;
            vector<int> edges;
     
            while(true){
                auto [p,pid] = par[u];
                if(p == -1) break;
                edges.pb(pid);
                u = p;
                if(good[u]){
                    ok = false;
                    break;
                }
            }
     
            if(!ok) conts;
     
            vector<int> seq;
            vector<int> v1;
     
            for(auto [v,id] : adj[i]){
                if(count(all(edges),id^1)) conts;
                v1.pb(id);
            }
     
            assert(sz(v1) >= 2);
            while(sz(v1) > 2) v1.pop_back();
     
            int x = v1[0], y = v1[1];
            seq = {x,x^1,y,y^1,x^1,x,y^1,y};
            
            ans = edges;
            reverse(all(ans));
            trav(x,seq) ans.pb(x);
            trav(x,edges) ans.pb(x);
            
            return ans;
        }

        assert(0);
    }

    vector<pii> edges = {
        {0,1},
        {1,0},
        {0,2},
        {2,0},
        {1,0},
        {0,1},
        {2,0},
        {0,2}
    };

    vector<int> ans;
    for(auto [u,v] : edges){
        for(auto [vv,idd] : adj[u]){
            if(vv == v){
                ans.pb(idd);
                break;
            }
        }
    }

    return ans;
}

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