Submission #828403

#	Time	Username	Problem	Language	Result	Execution time	Memory
828403		serifefedartar	Cat in a tree (BOI17_catinatree)	C++17	100 / 100	363 ms	39928 KiB

catinatree

#include <bits/stdc++.h>
using namespace std;
 
#define fast ios::sync_with_stdio(0);cin.tie(0);
typedef long long ll;
#define f first
#define s second
#define MOD 998244353
#define LOGN 18
#define MAXN 200005

vector<int> graph[MAXN];
vector<int> nearest;
int up[LOGN][MAXN], depth[MAXN], par[MAXN], sz[MAXN];
bool marked[MAXN];

void dfs(int node, int parent) {
	for (auto u : graph[node]) {
		if (u == parent)
			continue;
		depth[u] = depth[node] + 1;
		up[0][u] = node;
		for (int i = 1; i < LOGN; i++)
			up[i][u] = up[i-1][up[i-1][u]];
		dfs(u, node);
	}
}

int find(int node, int k) {
	for (int i = 0; i < LOGN; i++) {
		if ((1<<i) & k)
			node = up[i][node];
	}
	return node;
}

int lca(int a, int b) {
	if (depth[b] > depth[a])
		swap(a, b);
	a = find(a, depth[a] - depth[b]);
	if (a == b)
		return a;
	for (int i = LOGN-1; i >= 0; i--) {
		if (up[i][a] != up[i][b]) {
			a = up[i][a];
			b = up[i][b];
		}
	}
	return up[0][a];
}

int dist(int a, int b) {
	return depth[a] + depth[b] - 2*depth[lca(a, b)];
}
	
int get_sz(int node, int parent) {
	sz[node] = 1;
	for (auto u : graph[node]) {
		if (u == parent || marked[u])
			continue;
		sz[node] += get_sz(u, node);
	}
	return sz[node];
}

int find_centro(int node, int parent, int n) {
	for (auto u : graph[node]) {
		if (u == parent || marked[u])
			continue;
		if (sz[u] * 2 > n)
			return find_centro(u, node, n);
	}
	return node;
}

void decompose(int node, int parent) {
	int n = get_sz(node, parent);
	int centro = find_centro(node, node, n);

	par[centro] = parent;
	marked[centro] = true;
	for (auto u : graph[centro]) {
		if (!marked[u])
			decompose(u, centro);
	}
}

int main() {
	fast
	memset(par, -1, sizeof(par));
	int N, D;
	cin >> N >> D;

	nearest = vector<int>(N, 1e9);
	for (int i = 1; i < N; i++) {
		int x; cin >> x;
		graph[x].push_back(i);
		graph[i].push_back(x);
	}
	for (int i = 0; i < LOGN; i++)
		up[i][0] = 0;
	dfs(0, 0);
	decompose(0, -1);

	vector<pair<int,int>> order;
	for (int i = 0; i < N; i++)
		order.push_back({depth[i], i});
	sort(order.rbegin(), order.rend());

	int ans = 0;
	for (auto u : order) {
		int node = u.s;
		int now = node;
		int mn_dist = 1e9;
		while (now != -1) {
			mn_dist = min(mn_dist, dist(node, now) + nearest[now]);
			now = par[now];
		}

		if (mn_dist >= D) {
			ans++;
			int now = node;
			while (now != -1) {
				nearest[now] = min(nearest[now], dist(node, now));
				now = par[now];
			}
		}
	}
	cout << ans << "\n";
}

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