Submission #1064002

#	Time	Username	Problem	Language	Result	Execution time	Memory
1064002		BF001	Railway (BOI17_railway)	C++17	100 / 100	68 ms	26572 KiB

railway

#include<bits/stdc++.h>
using namespace std;
 
#define N 100005
#define log 17
#define fi first
#define se second

typedef pair<int, int> ii;

int n, m, k, par[log + 2][N], tin[N], tout[N], tim, dp[N];
vector<ii> adj[N];
vector<int> res;
 
void dfs(int u, int p){
    tin[u] = ++tim;
    for (auto x : adj[u]){
        int v = x.fi;
        if (v == p) continue;
        par[0][v] = u;
        dfs(v, u);
    }
    tout[u] = tim;
}

bool in(int u, int v){
    return (tin[u] <= tin[v] && tout[v] <= tout[u]);
}

int getlca(int u, int v){
    if (in(u, v)) return u;
    if (in(v, u)) return v;
    for (int k = log; k >= 0; k--){
        if (par[k][u] && !in(par[k][u], v)) u = par[k][u];
    }
    return par[0][u];
}

bool cmp(int&a, int& b){
    return tin[a] < tin[b];
}

void dfs2(int u, int p){
    for (auto x : adj[u]){
        int v = x.fi, idx = x.se;
        if (v == p) continue;
        dfs2(v, u);
        if (dp[v] >= k) res.push_back(idx);
        dp[u] += dp[v];
    }
}

signed main(){
    ios_base::sync_with_stdio(0);
    cin.tie(NULL);
 
    cin >> n >> m >> k;
    for (int i = 1; i <= n - 1; i++){
        int u, v;
        cin >> u >> v;
        adj[u].push_back({v, i});
        adj[v].push_back({u, i});
    }

    dfs(1, 0);
    for (int j = 1; j <= log; j++){
        for (int i = 1; i <= n; i++) par[j][i] = par[j - 1][par[j - 1][i]];
    }

    for (int i = 1; i <= m; i++){
        int num;
        cin >> num;
        vector<int> vec;
        for (int j = 1; j <= num; j++){
            int val;
            cin >> val;
            vec.push_back(val);
        }
        sort(vec.begin(), vec.end(), cmp);
        int lst = -1;
        dp[getlca(vec[0], vec[num - 1])]--;
        for (auto x : vec){
            dp[x]++;
            if (lst != -1) dp[getlca(x, lst)]--;
            lst = x;
        }
    }

    dfs2(1, 0);
   /// for (int i = 1; i <= n; i++) cout << i << " :  "  << dp[i] << "\n";

    sort(res.begin(), res.end());

    cout << (int) res.size() << "\n";
    for (auto x : res) cout << x << ' ';

    return 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