Submission #747695

#	Time	Username	Problem	Language	Result	Execution time	Memory
747695		GrindMachine	Cat in a tree (BOI17_catinatree)	C++17	100 / 100	485 ms	45536 KiB

catinatree

// 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

/*



*/

const int MOD = 1e9 + 7;
const int N = 2e5 + 5;
const int inf1 = int(1e9) + 5;
const ll inf2 = ll(1e18) + 5;

vector<int> 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));
        depth = vector<int>(n + 1);

        lca_dfs(0, -1);
    }

    void lca_dfs(int node, int par) {
        trav(child, 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];
    }
};

vector<int> subsiz(N);
vector<bool> rem(N);
vector<int> par(N);

int get_siz(int u, int p){
    subsiz[u] = 1;
    trav(v,adj[u]){
        if(v == p or rem[v]) conts;
        subsiz[u] += get_siz(v,u);
    }
    return subsiz[u];
}

int get_centroid(int u, int p, int nodes){
    trav(v, adj[u]){
        if(v == p or rem[v]) conts;
        if(subsiz[v] > nodes / 2){
            return get_centroid(v,u,nodes);
        }
    }

    return u;
}

void build(int u, int p){
    int nodes = get_siz(u,-1);
    int centroid = get_centroid(u,-1,nodes);

    par[centroid] = p;
    rem[centroid] = 1;

    trav(v, adj[centroid]){
        if(rem[v]) conts;
        build(v,centroid);
    }
}

void solve(int test_case)
{
    int n,d; cin >> n >> d;
    rep1(i,n){
        int p; cin >> p;
        adj[p].pb(i), adj[i].pb(p);
    }

    lca_algo LCA(n);
    build(0,-1);

    vector<pii> order;
    rep(i,n){
        order.pb({LCA.depth[i],i});
    }

    sort(rall(order));

    vector<int> best(n,inf1);
    int ans = 0;

    for(auto [dep, u] : order){
        // find closest active guy
        // similar to cf xenia and tree
        int mnd = inf1;
        int lca = u;

        while(lca != -1){
            int du = LCA.get_dis(u,lca);
            int d = du + best[lca];
            amin(mnd, d);
            lca = par[lca];
        }

        if(mnd >= d){
            // activate
            ans++;

            lca = u;
            while(lca != -1){
                int du = LCA.get_dis(u,lca);
                amin(best[lca], du);
                lca = par[lca];
            }
        }
    }

    cout << ans << endl;
}

int main()
{
    fastio;

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

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

    return 0;
}

• Subtask 1: 11 / 11
• Subtask 2: 40 / 40
• Subtask 3: 49 / 49