Submission #378287

#	Time	Username	Problem	Language	Result	Execution time	Memory
378287		Sara	Railway (BOI17_railway)	C++14	100 / 100	278 ms	66152 KiB

railway

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

typedef long long ll;
typedef long double ld;

#define pb push_back
#define F first
#define S second
 
const int N = 300000 + 5;
const int LOG = 30;

int n, m, k;
vector < pair <int, int> > g[N];

int par[LOG][N], h[N];

vector <int> ans;
set <int> st[N];
vector <int> out[N];

void dfs(int v, int pr){
    for (auto it : g[v]){
        int u = it.F;
        if (u == pr) continue;
        par[0][u] = v; 
        h[u] = h[v] + 1;
        dfs(u, v);
    }
    return;
}

inline void pre(){
    for (int i = 1; i < LOG; i ++){
        for (int v = 1; v <= n; v ++){
            par[i][v] = par[i - 1][par[i - 1][v]];
        }
    }
    return;
}

inline int get_par(int v, int dif){
    for (int i = 0; i < LOG; i ++){
        if ((dif >> i & 1)){
            v = par[i][v];
        }
    }
    return v;
}

inline int LCA(int u, int v){
    if (h[v] < h[u]) swap(u, v);
    v = get_par(v, h[v] - h[u]);
    if (u == v) return v;
    for (int i = LOG - 1; i >= 0; i --){
        if (par[i][u] != par[i][v]){
            u = par[i][u];
            v = par[i][v];
        }
    }
    return par[0][v];
}

inline void merge(int pr, int v){
    if ((int)st[pr].size() < (int)st[v].size()){
        swap(st[pr], st[v]);
    }
    for (int col : st[v]){
        st[pr].insert(col);
    }
    st[v].clear();
    return;
}

inline void del(int v){
    for (int col : out[v]){
        st[v].erase(st[v].lower_bound(col));
    }
    return;
}

void dfsCalc(int v, int pr){
    for (auto it : g[v]){
        int u = it.F;
        int id = it.S;
        if (id == pr) continue;
        dfsCalc(u, id);
        merge(v, u);
    }
    del(v);
    if ((v != 1) && (k <= (int)st[v].size())) ans.pb(pr);
    return;
}

int main() {
    ios_base::sync_with_stdio(0), cin.tie(0); cout.tie(0);
    cin >> n >> m >> k;
    for (int i = 1; i < n; i ++){
        int u, v;
        cin >> u >> v;
        g[u].pb({v, i}); g[v].pb({u, i});
    }
    dfs(1, 0); pre();
    for (int i = 1; i <= m; i ++){
        int sz, v, lca = 0;
        cin >> sz;
        vector <int> C = {};

        for (int j = 0; j < sz; j ++){
            int v;
            cin >> v;
            C.pb(v);
            if (lca == 0){
                lca = C[j];
            }
            else {
                lca = LCA(lca, C[j]);
            }
        }

        out[lca].pb(i);
        for (int u: C){
            st[u].insert(i);
        }
        //cout << "dbg " << i << ' ' << lca << '\n';
    }
    dfsCalc(1, 0);
    sort(ans.begin(), ans.end());
    cout << (int)ans.size() << '\n';
    for (int i : ans) cout << i << ' ';
    return 0;
}

Compilation message (stderr)

railway.cpp: In function 'int main()':
railway.cpp:106:17: warning: unused variable 'v' [-Wunused-variable]
  106 |         int sz, v, lca = 0;
      |                 ^

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