Submission #394530

#	Time	Username	Problem	Language	Result	Execution time	Memory
394530		couplefire	Pastiri (COI20_pastiri)	C++17	100 / 100	961 ms	150640 KiB

pastiri

#include <bits/stdc++.h>
using namespace std;
#define MAXN 500005

int n, k;
vector<int> adj[MAXN];
vector<int> newadj[MAXN];
int dist[MAXN], good[MAXN], depth[MAXN];
bool sheep[MAXN], visited[MAXN];
vector<int> curstack[2*MAXN];
set<array<int, 2>, greater<array<int, 2>>> active;
vector<int> ans;

void bfs(){
    memset(dist, 63, sizeof dist);
    queue<int> q;
    for(int i = 0; i<n; i++) if(sheep[i]) q.push(i), dist[i] = 0;
    while(!q.empty()){
        int v = q.front(); q.pop();
        for(auto u : adj[v]) if(dist[u] > dist[v]+1) dist[u] = dist[v]+1, q.push(u);
    }
}

void dfs(int v, int p, int d){
    depth[v] = d;
    curstack[depth[v]+dist[v]].push_back(v);
    if(sheep[v]) good[v] = curstack[depth[v]+dist[v]].front();
    for(auto u : adj[v]){
        if(u == p) continue;
        dfs(u, v, d+1);
    }
    curstack[depth[v]+dist[v]].pop_back();
}

void deactive(int v){
    visited[v] = 1;
    if(sheep[v]) active.erase({depth[v], v});
    for(auto u : newadj[v]){
        if(visited[u]) continue;
        deactive(u);
    }
}

int main(){
    // freopen("a.in", "r", stdin);
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cin >> n >> k;
    for(int i = 0; i<n-1; i++){
        int a, b; cin >> a >> b; --a; --b;
        adj[a].push_back(b);
        adj[b].push_back(a);
    }
    for(int i = 0; i<k; i++){
        int a; cin >> a; --a;
        sheep[a] = 1;
    }
    bfs();
    dfs(0, 0, 0);
    for(int v = 0; v<n; v++){
        for(auto u : adj[v]) if(dist[u] == dist[v]-1) newadj[v].push_back(u);
    }
    for(int v = 0; v<n; v++){
        if(sheep[v]) active.insert({depth[v], v});
    }
    while(!active.empty()){
        int v = (*active.begin())[1];
        ans.push_back(good[v]);
        deactive(good[v]);
    }
    cout << ans.size() << endl;
    for(auto x : ans) cout << x+1 << " ";
    cout << endl;
}

• Subtask 1: 8 / 8
• Subtask 2: 18 / 18
• Subtask 3: 23 / 23
• Subtask 4: 51 / 51