Submission #649175

#	Time	Username	Problem	Language	Result	Execution time	Memory
649175		LeonaRaging	Cat in a tree (BOI17_catinatree)	C++14	0 / 100	4 ms	5716 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], up[maxn][20], par[maxn], mn[maxn];
vector<int> adj[maxn], nodes;
bool used[maxn];

void dfs(int u, int p) {
    up[u][0] = p;
    for (int j = 1; j <= N; j++)
        up[u][j] = up[up[u][j - 1]][j - 1];
    for (int v : adj[u])
        if (v != p) {
            h[v] = h[u] + 1;
            dfs(v, u);
        }
}

int lca(int u, int v) {
    if (h[u] < h[v]) swap(u, v);
    int k = h[u] - h[v];
    for (int j = N; j >= 0; j--)
        if (k >> j & 1)
            u = up[u][j];
    if (u == v) return u;
    for (int j = N; j >= 0; j--)
        if (up[u][j] != up[v][j])
            u = up[u][j], v = up[v][j];
    return up[u][0];
}

int dis(int u, int v) {
    return h[u] + h[v] - 2 * h[lca(u, v)];
}

void update(int u) {
    for (int v = u; v != 0; v = par[v])
        mn[v] = min(mn[v], dis(v, u));
}

bool ok(int u) {
    for (int v = u; v != 0; v = par[v]) {
        if (mn[v] + dis(u, v) < d) return 0;
    }
    return 1;
}

struct Centroid_Decomposition {
    int sz[maxn];
    int dfs(int u) {
        sz[u] = 1;
        for (int v : adj[u])
            if (v != up[u][0] && !used[v])
                sz[u] += dfs(v);
        return sz[u];
    }
    int Centroid(int u, int tot) {
        for (int v : adj[u])
            if (v != up[u][0] && !used[v] && sz[v] > tot / 2)
                return Centroid(v, tot);
        return u;
    }
    void build(int u = 1) {
        int c = Centroid(u, dfs(u));
        used[c] = 1;
        for (int v : adj[c]) 
            if (!used[v]) {
                par[v] = c;
                build(v);
            }
    }
} 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();
    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) {
        if (ok(u)) {
            res++;
            update(u);
        }
    }   
    cout << res;
}

• Subtask 1: 0 / 11
• Subtask 2: 0 / 40
• Subtask 3: 0 / 49