Submission #1126742

#	Time	Username	Problem	Language	Result	Execution time	Memory
1126742		doducanh	Railway (BOI17_railway)	C++20	100 / 100	73 ms	23268 KiB

railway

///roadtoVOI2025
///enjoythejourney
#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define fi first
#define se second
#define ii pair<int,int>
#define mp make_pair
#define in(x) freopen(x,"r",stdin)
#define out(x) freopen(x,"w",stdout)
#define bit(x,i) ((x>>i)&1)
#define lc (id<<1)
#define rc ((id<<1)^1)
const int maxn=1e5+7;
vector<ii>adj[maxn];
int p[25][maxn];
int in[maxn],out[maxn];
int h[maxn];
int cnt=0;
int n,m,k;
int t[maxn];
int dinh[maxn];
void dfs(int u,int par)
{
    in[u]=++cnt;
    for(auto [v,id]:adj[u])if(v!=par){
        p[0][v]=u;
        dinh[v]=id;
        h[v]=h[u]+1;
        dfs(v,u);
    }
    out[u]=cnt;
}
int lca(int u,int v)
{
    if(h[u]<h[v])swap(u,v);
    int diff=h[u]-h[v];
    for(int i=20;i>=0;i--)if(bit(diff,i))u=p[i][u];
    if(u==v)return u;
    for(int i=20;i>=0;i--)if(p[i][u]!=p[i][v]){
        u=p[i][u];
        v=p[i][v];
    }
    return p[0][u];
}
void up(int x,int val)
{
    for(;x<maxn;x+=(x&(-x)))t[x]+=val;
}
int get(int x)
{
    int res=0;
    if(x<=0)return 0;
    for(;x;x-=(x&(-x)))res+=t[x];
    return res;
}
void sol()
{
    cin>>n>>m>>k;
    for(int i=1;i<n;i++){
        int u,v;
        cin>>u>>v;
        adj[u].push_back({v,i});
        adj[v].push_back({u,i});
    }
    dfs(1,0);
    for(int i=1;i<=20;i++){
        for(int j=1;j<=n;j++){
            p[i][j]=p[i-1][p[i-1][j]];
        }
    }
    for(int i=1;i<=m;i++){
        int s;
        cin>>s;
        vector<int>v;
        for(int j=1;j<=s;j++){
            int x;
            cin>>x;
            v.push_back(x);
        }
        sort(v.begin(),v.end(),[&](const int &a,const int &b){
             return in[a]<in[b];
        });
        v.push_back(v[0]);
        for(int i=0;i<v.size()-1;i++){
            int l=lca(v[i],v[i+1]);
            up(in[v[i]],1);
            up(in[v[i+1]],1);
            up(in[l],-2);
        }
    }
    vector<int>ans;
    for(int i=1;i<=n;i++){
        if(get(out[i])-get(in[i]-1)>=2*k)ans.push_back(dinh[i]);
    }
    sort(ans.begin(),ans.end());
    cout<<ans.size()<<"\n";
    for(int x:ans){
        cout<<x<<" ";
    }
}
signed main(void)
{
    ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    int t=1;
    while(t--){
        sol();
    }
    // you should actually read the stuff at the bottom
    return 0;
}
/* stuff you should look for
 * int overflow, array bounds
 * special cases (n=1?)
 * do smth instead of nothing and stay organized
 * WRITE STUFF DOWN
 * DON'T GET STUCK ON ONE APPROACH
 */

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