Submission #710713

#	Time	Username	Problem	Language	Result	Execution time	Memory
710713		Jarif_Rahman	Thousands Islands (IOI22_islands)	C++17	35 / 100	463 ms	46568 KiB

islands

#include "islands.h"
#include <bits/stdc++.h>
#define pb push_back
#define f first
#define sc second
using namespace std;
typedef long long int ll;
typedef string str;

int n, m, k;
vector<int> U, V;
vector<vector<int>> initial_graph;
vector<bool> reachable;

vector<set<int>> in(n), out(n);
set<pair<int, int>> st;

void dfs_reachability(int nd){
    if(reachable[nd]) return;
    reachable[nd] = 1;
    for(int x: initial_graph[nd]) dfs_reachability(x);
}

void remove_node(int nd){
    st.erase({out[nd].size(), nd});

    for(int i: in[nd]){
        st.erase({out[U[i]].size(), U[i]});
        out[U[i]].erase(i);
        st.insert({out[U[i]].size(), U[i]});
    }
    for(int i: out[nd]) in[V[i]].erase(i);
    out[nd].clear();
    in[nd].clear();
}

void preprocess(){
    in.resize(n);
    out.resize(n);
    for(int i = 0; i < m; i++){
        if(!reachable[U[i]] || !reachable[V[i]]) continue;
        out[U[i]].insert(i);
        in[V[i]].insert(i);
    }

    for(int i = 0; i < n; i++){
        st.insert({out[i].size(), i});
    }

    while(!st.empty() && st.begin()->f == 0) remove_node(st.begin()->sc);
};


variant<bool, vector<int>> find_journey(int _n, int _m, vector<int> _U, vector<int> _V){
    n = _n, m = _m, U = _U, V = _V;

    initial_graph.assign(n, {});
    reachable.assign(n, 0);

    for(int i = 0; i < m; i++) initial_graph[U[i]].pb(V[i]);

    dfs_reachability(0);
    preprocess();

    set<int> cur = {0};

    int ND = -1;
    while(!cur.empty()){
        for(int x: cur){
            if(out[x].size() >= 2) ND = x;
        }
        if(ND != -1) break;
        set<int> _cur;
        for(int x: cur) for(int i: out[x]) _cur.insert(V[i]);
        for(int x: cur) remove_node(x);
        while(!st.empty() && st.begin()->f == 0) remove_node(st.begin()->sc);
        swap(cur, _cur);
    }

    if(ND == -1) return false;
    return true;
}

• Subtask 1: 1.75 / 5
• Subtask 2: 1.75 / 5
• Subtask 3: 7.35 / 21
• Subtask 4: 8.399999999999999 / 24
• Subtask 5: 15.749999999999998 / 45