Submission #681123

#	Time	Username	Problem	Language	Result	Execution time	Memory
681123		Ronin13	Railway (BOI17_railway)	C++14	100 / 100	184 ms	32344 KiB

railway

#include <bits/stdc++.h>
#define ll long long
#define ull unsigned ll
#define f first
#define s second
#define pii pair<ll,ll>
#define pll pair<ll,ll>
#define pb push_back
#define epb emplace_back
using namespace std;

const int nmax = 2e5 + 1;
vector <vector <int> > g(nmax);
vector <pii> edges;
int a[nmax][22];
int in[nmax], out[nmax];
int timer = 0;

void prepare_dfs(int v, int e = 0){
    a[v][0] = e;
    in[v] = timer++;
    for(int j = 1; j <= 20; j++)
        if(a[v][j - 1]) a[v][j] = a[a[v][j - 1]][j - 1];
    for(int to : g[v]){
        to = edges[to].f + edges[to].s - v;
        if(to == e) continue;
        prepare_dfs(to, v);
    }
    out[v] = timer++;
}

bool is_ancestor(int u, int v){
    return (!u) || (in[u] < in[v] && out[u] > out[v]);
}

int lca(int x, int y){
    if(is_ancestor(x, y))
        return x;
    if(is_ancestor(y, x))
        return y;
    for(int j = 20; j >= 0; j--){
        if(is_ancestor(a[x][j], y)) continue;
        x = a[x][j];
    }
    return a[x][0];
}

int cnt[nmax];

vector <int> ans;
int k;
void DFS(int v, int e = 0){
    for(int to : g[v]){
        int x = to + 1;
        to = edges[to].f + edges[to].s - v;
        if(to == e) {

            continue;
        }

        DFS(to, v);
        if(cnt[to] >= k) ans.pb(x);

        cnt[v] += cnt[to];
    }
}


int main(){
    //ios_base::sync_with_stdio(false); cin.tie(0);
    int n, m; cin >> n >> m >> k;
    for(int i = 0; i < n - 1; i++){
        int u, v; cin >> u >> v;
        g[u].pb(i);
        g[v].pb(i);
        edges.pb({u, v});
    }
    prepare_dfs(1);
    while(m--){
        int l; cin >> l;
        vector <pii> vec;
        for(int i= 0; i < l; i++){
            int x; cin >> x;
            vec.pb({in[x], x});
        }
        sort(vec.begin(), vec.end());
        for(int i = 0; i < l - 1; i++){
            int x = vec[i].s, y = vec[i + 1].s;
            int u = lca(x, y);
            vec.pb({in[u], u});
        }
        sort(vec.begin(), vec.end());
        stack <int> st;
        st.push(vec[0].s);
        for(int i = 1; i < vec.size(); i++){
            int x = vec[i].s;
            //cout << x << " ";
            if(x == vec[i - 1].s) continue;
            while(!st.empty()){
                int v = st.top();
                if(out[v] < out[x]) st.pop();
                else break;
            }
            vec[i].f = st.top();
            st.push(x);
        }
      //  cout << "\n";
        for(int i = 1; i < vec.size(); i++){
            if(vec[i].s == vec[i - 1].s) continue;
            int x = vec[i].f, y = vec[i].s;
            cnt[x]--, cnt[y]++;
        }
       // cout <<"\n";
    }

    DFS(1);
    cout << ans.size() << "\n";
    sort(ans.begin(), ans.end());
    for(int to : ans) cout << to << ' ';
    return 0;
}

Compilation message (stderr)

railway.cpp: In function 'int main()':
railway.cpp:95:26: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<long long int, long long int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   95 |         for(int i = 1; i < vec.size(); i++){
      |                        ~~^~~~~~~~~~~~
railway.cpp:108:26: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<long long int, long long int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  108 |         for(int i = 1; i < vec.size(); i++){
      |                        ~~^~~~~~~~~~~~

• Subtask 1: 8 / 8
• Subtask 2: 15 / 15
• Subtask 3: 7 / 7
• Subtask 4: 29 / 29
• Subtask 5: 16 / 16
• Subtask 6: 25 / 25