Submission #747129

#	Time	Username	Problem	Language	Result	Execution time	Memory
747129		GrindMachine	Railway (BOI17_railway)	C++17	100 / 100	271 ms	34700 KiB

railway

// Om Namah Shivaya

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace std;
using namespace __gnu_pbds;

template<typename T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
typedef long long int ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL)
#define pb push_back
#define endl '\n'
#define sz(a) a.size()
#define setbits(x) __builtin_popcountll(x)
#define ff first
#define ss second
#define conts continue
#define ceil2(x, y) ((x + y - 1) / (y))
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define yes cout << "Yes" << endl
#define no cout << "No" << endl

#define rep(i, n) for(int i = 0; i < n; ++i)
#define rep1(i, n) for(int i = 1; i <= n; ++i)
#define rev(i, s, e) for(int i = s; i >= e; --i)
#define trav(i, a) for(auto &i : a)

template<typename T>
void amin(T &a, T b) {
    a = min(a, b);
}

template<typename T>
void amax(T &a, T b) {
    a = max(a, b);
}

#ifdef LOCAL
#include "debug.h"
#else
#define debug(x) 42
#endif

/*

refs:
https://cp-algorithms.com/graph/hld.html (hld tutorial)

*/

const int MOD = 1e9 + 7;
const int N = 1e5 + 5;
const int inf1 = int(1e9) + 5;
const ll inf2 = ll(1e18) + 5;

vector<pll> adj[N];

struct lca_algo {
    // LCA template (for graphs with 1-based indexing)

    int LOG = 1;
    vector<int> depth;
    vector<vector<int>> up;

    lca_algo() {

    }

    lca_algo(int n) {
        lca_init(n);
    }

    void lca_init(int n) {
        while ((1 << LOG) < n) LOG++;
        up = vector<vector<int>>(n + 1, vector<int>(LOG, 1));
        depth = vector<int>(n + 1);

        lca_dfs(1, -1);
    }

    void lca_dfs(int node, int par) {
        for(auto [child, id] : adj[node]) {
            if (child == par) conts;

            up[child][0] = node;
            rep1(j, LOG - 1) {
                up[child][j] = up[up[child][j - 1]][j - 1];
            }

            depth[child] = depth[node] + 1;

            lca_dfs(child, node);
        }
    }

    int lift(int u, int k) {
        rep(j, LOG) {
            if (k & (1 << j)) {
                u = up[u][j];
            }
        }

        return u;
    }

    int query(int u, int v) {
        if (depth[u] < depth[v]) swap(u, v);
        int k = depth[u] - depth[v];
        u = lift(u, k);

        if (u == v) return u;

        rev(j, LOG - 1, 0) {
            if (up[u][j] != up[v][j]) {
                u = up[u][j];
                v = up[v][j];
            }
        }

        u = up[u][0];
        return u;
    }

    int get_dis(int u, int v) {
        int lca = query(u, v);
        return depth[u] + depth[v] - 2 * depth[lca];
    }
};

template<typename T>
struct fenwick {
    int siz;
    vector<T> tree;

    fenwick(int n) {
        siz = n;
        tree = vector<T>(n + 1);
    }

    int lsb(int x) {
        return x & -x;
    }

    void build(vector<T> &a, int n) {
        for (int i = 1; i <= n; ++i) {
            int par = i + lsb(i);
            tree[i] += a[i];

            if (par <= siz) {
                tree[par] += tree[i];
            }
        }
    }

    void pupd(int i, T v) {
        while (i <= siz) {
            tree[i] += v;
            i += lsb(i);
        }
    }

    T sum(int i) {
        T res = 0;

        while (i) {
            res += tree[i];
            i -= lsb(i);
        }

        return res;
    }

    T query(int l, int r) {
        if (l > r) return 0;
        T res = sum(r) - sum(l - 1);
        return res;
    }
};

vector<ll> tin(N), tout(N);
vector<ll> depth(N), subsiz(N);
vector<pll> par(N);
ll timer = 1;

void dfs(ll u, ll p){
    tin[u] = timer++;
    subsiz[u] = 1;
    
    for(auto [v, id] : adj[u]) {
        if(v == p) conts;
        par[v] = {u, id};
        depth[v] = depth[u] + 1;
    
        dfs(v,u);

        subsiz[u] += subsiz[v];
    }

    tout[u] = timer++;
}

vector<ll> head(N), pos(N);
ll curr_pos = 1;

void decompose(ll u, ll p, ll h){
    head[u] = h;
    pos[u] = curr_pos++;

    ll mx = -1, heavy = -1;
    for(auto [v, id] : adj[u]){
        if(v == p) conts;
        if(subsiz[v] > mx){
            mx = subsiz[v];
            heavy = v;
        }
    }

    if(heavy != -1){
        decompose(heavy, u, h);
    }

    for(auto [v, id] : adj[u]){
        if(v == p or v == heavy) conts;
        decompose(v, u, v);
    }
}

fenwick<ll> fenw(N);

void upd(ll u, ll v, ll add){
    for(; head[u] != head[v]; v = par[head[v]].ff){
        if(depth[u] > depth[v]){
            swap(u,v);
        }

        fenw.pupd(pos[head[v]], add);
        fenw.pupd(pos[v] + 1, -add);
    }

    if(pos[u] > pos[v]){
        swap(u,v);
    }

    fenw.pupd(pos[u], add);
    fenw.pupd(pos[v] + 1, -add);
}

void solve(int test_case)
{
    ll n,m,need; cin >> n >> m >> need;
    rep1(i,n-1){
        ll u,v; cin >> u >> v;
        adj[u].pb({v, i}), adj[v].pb({u, i});
    }

    dfs(1,-1);
    decompose(1,-1,1);
    lca_algo LCA(n);

    // auto upd = [&](ll u, ll v){
    //     while(u != v){
    //         auto [p, id] = par[u];
    //         cnt[id]++;
    //         u = p;
    //     }
    // };

    while(m--){
        ll k; cin >> k;
        vector<pll> a(k);
        rep(j,k){
            ll u; cin >> u;
            a[j] = {tin[u], u};
        }

        sort(all(a));

        vector<pll> b;
        rep(i,k){
            b.pb({depth[a[i].ss], a[i].ss});
            if(i+1 < k){
                ll lca = LCA.query(a[i].ss, a[i+1].ss);
                b.pb({depth[lca], lca});
            }
        }

        sort(rall(b));
        b.resize(unique(all(b)) - b.begin());
        
        set<pll> st;
        for(auto [d, u] : b){
            ll l = tin[u], r = tout[u];
            auto it = st.lower_bound({l,-1});
            vector<pll> torem;

            for(; it != st.end() and it->first <= r; ++it){
                torem.pb(*it);
                upd(it->second, u, 1);
                upd(u,u,-1);
            }

            trav(p,torem){
                st.erase(p);
            }

            st.insert({tin[u], u});
        }

        assert(sz(st) == 1);
    }

    vector<ll> ans;

    rep1(u,n){
        if(u == 1) conts;

        ll id = par[u].ss;
        ll cnt = fenw.query(1, pos[u]);

        if(cnt >= need){
            ans.pb(id);
        }
    }

    sort(all(ans));

    cout << sz(ans) << endl;
    trav(x,ans) cout << x << " ";
    cout << endl;
}

int main()
{
    fastio;

    int t = 1;
    // cin >> t;

    rep1(i, t) {
        solve(i);
    }

    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