Submission #649178

#	Time	Username	Problem	Language	Result	Execution time	Memory
649178		LeonaRaging	Cat in a tree (BOI17_catinatree)	C++14	100 / 100	338 ms	36296 KiB

catinatree

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

#define fi first
#define se second
#define ll long long
#define pb push_back
#define db(val) "[" #val " = " << (val) << "] "

const ll mod = 1e9 + 7;
const int maxn = 2e5 + 4;
const int INF = 1e9;
const int N = 18;

int n, d, h[maxn], par[maxn], mn[maxn], dis[maxn][20], cen_dep[maxn];
vector<int> adj[maxn], nodes;
bool used[maxn];

void dfs(int u, int p) {
    for (int v : adj[u])
        if (v != p) {
            h[v] = h[u] + 1;
            dfs(v, u);
        }
}

void Solve(int u, int p, int dep, int c) {
    dis[u][c] = dep;
    for (int v : adj[u])
        if (v != p && !used[v]) 
            Solve(v, u, dep + 1, c);
}

struct Centroid_Decomposition {
    int sz[maxn];
    int dfs(int u, int p) {
        sz[u] = 1;
        for (int v : adj[u])
            if (v != p && !used[v])
                sz[u] += dfs(v, u);
        return sz[u];
    }
    int Centroid(int u, int p, int tot) {
        for (int v : adj[u])
            if (v != p && !used[v] && sz[v] > tot / 2)
                return Centroid(v, u, tot);
        return u;
    }
    void build(int u, int p, int dep) {
        int c = Centroid(u, 0, dfs(u, 0));
        cen_dep[c] = dep;
        Solve(c, 0, 0, dep);
        used[c] = 1;
        par[c] = p;
        for (int v : adj[c]) 
            if (!used[v])
                build(v, c, dep + 1);
    }
} Cen;

int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    //freopen(".INP", "r", stdin);
    //freopen(".OUT", "w", stdout);
    cin >> n >> d;
    for (int u = 2; u <= n; u++) {
        int v; cin >> v; v++;
        adj[u].pb(v);
        adj[v].pb(u);
    }
    dfs(1, 0);
    Cen.build(1, 0, 0);
    for (int u = 1; u <= n; u++)
        nodes.pb(u);
    sort(nodes.begin(), nodes.end(),[&](int u, int v) {
        return h[u] > h[v];
    });
    int res = 0;
    memset(mn, 63, sizeof mn);
    for (int u : nodes) {
        int dep = mn[0], v = u;
        while (v) {
            dep = min(dep, dis[u][cen_dep[v]] + mn[v]);
            v = par[v];
        }
        if (dep < d) continue;
        res++;
        v = u;
        while (v) {
            mn[v] = min(mn[v], dis[u][cen_dep[v]]);
            v = par[v];
        }
    }   
    cout << res;
}

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