이 제출은 이전 버전의 oj.uz에서 채점하였습니다. 현재는 제출 당시와는 다른 서버에서 채점을 하기 때문에, 다시 제출하면 결과가 달라질 수도 있습니다.
#include <bits/stdc++.h>
using namespace std;
// #define int long long
#ifdef LOCAL
#include "algo/debug.h"
#else
#define debug(...) 42
#endif
#define all(a) (a).begin(), (a).end()
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define reps(i, s, n) for (int i = s; i < (n); ++i)
#define pb push_back
#define sz(a) (int) (a.size())
const int N = 2e5 + 5;
const int inf = 1e9;
vector<int> g[N];
vector<pair<int, int>> centroids[N];
int s[N], mdist[N], used[N], res, d, m;
void sizes(int v, int p) {
s[v] = 1;
for (auto &u : g[v]) {
if (u != p && !used[u]) {
sizes(u, v);
s[v] += s[u];
}
}
}
int centroid(int v, int p, int n) {
for (auto &u : g[v]) {
if (u != p && !used[u] && s[u] > n / 2) {
return centroid(u, v, n);
}
}
return v;
}
int vis[N], dis[N], q[N], from, to, vs[N];
void decomposition1(int v) {
used[v] = 1;
sizes(v, -1);
m = 0;
from = 0;
to = 1;
dis[v] = 0;
q[0] = v;
while (from != to) {
int ver = q[from++];
vs[m++] = ver;
centroids[ver].emplace_back(v, dis[ver]);
vis[ver] = 1;
for (auto &u : g[ver]) {
if (!used[u] && !vis[u]) {
dis[u] = dis[ver] + 1;
q[to++] = u;
vis[u] = 1;
}
}
}
// for (int i = 0; i < m; i++) {
// vis[vs[i]] = 0;
// }
for (auto &u : g[v]) {
if (!used[u]) {
decomposition1(centroid(u, v, s[u]));
}
}
}
void decomposition2(int v) {
used[v] = 1;
sizes(v, -1);
m = 0;
from = 0;
to = 1;
dis[v] = 0;
q[0] = v;
while (from != to) {
int ver = q[from++];
vs[m++] = ver;
vis[ver] = 1;
for (auto &u : g[ver]) {
if (!used[u] && !vis[u]) {
dis[u] = dis[ver] + 1;
q[to++] = u;
vis[u] = 1;
}
}
}
auto can = [&] (int ver) -> bool {
for (auto &[centroid, dist_to_centroid] : centroids[ver]) {
if (dist_to_centroid + mdist[centroid] < d) {
return false;
}
}
return true;
};
int r = m, cnt = 0;
rep(l, m) {
while (r - 1 >= l && dis[vs[r - 1]] >= max(dis[vs[l]], d - dis[vs[l]])) {
r--;
int ver = vs[r];
if (can(ver)) {
cnt++;
for (auto &[centroid, dist_to_centroid] : centroids[ver]) {
mdist[centroid] = min(mdist[centroid], dist_to_centroid);
}
}
}
if (l == r) {
res = max(res, cnt);
break;
} else {
res = max(res, cnt + can(vs[l]));
}
}
for (int i = 0; i < m; i++) {
// vis[vs[i]] = 0;
for (auto &[centroid, dist_to_centroid] : centroids[vs[i]]) {
mdist[centroid] = inf;
}
}
for (auto &u : g[v]) {
if (!used[u]) {
decomposition2(centroid(u, v, s[u]));
}
}
}
void solve() {
fill(mdist, mdist + N, inf);
int n;
cin >> n >> d;
if (d > n - 1) {
cout << 1;
return;
}
if (d == 0) {
cout << n;
return;
}
reps(i, 1, n) {
int p;
cin >> p;
g[p].push_back(i);
g[i].push_back(p);
}
sizes(0, -1);
decomposition1(centroid(0, -1, n));
fill(used, used + N, 0);
sizes(0, -1);
decomposition2(centroid(0, -1, n));
cout << res;
}
signed main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
solve();
return 0;
}
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