Apple Tree

Apple Tree

SCUACM2022集训前训练-数据结构 - Virtual Judge (vjudge.net)

dfs序 + 树状数组

注意以后存边时写，效率较高

vector<vector<int> > G(N);

#include <iostream>
#include <cstring>
#include <algorithm>
#include <vector>
#include <cmath>
#include <cstdio>
using namespace std;
typedef long long ll;
const int N = 1e5 + 10;
vector<vector<int> > G(N);
int tim, tin[N], tout[N];
int tr[N];
int n;

int lowbit(int x)
{
	return x & -x;
}

int query(int idx)
{
	int ans = 0;
	for (int i = idx; i; i -= lowbit(i))
		ans += tr[i];
	return ans;
}

void add(int idx, int k)
{
	for (int i = idx; i <= n; i += lowbit(i))
		tr[i] += k;
}

void add_edge(int u, int v)
{
	G[u].push_back(v);
}

void dfs(int u, int fa)
{
	tin[u] = ++tim;
	for (int i = 0; i < G[u].size(); i++)
	{
		int v = G[u][i];
		if (v == fa)
			continue;
		dfs(v, u);
	}
	tout[u] = tim;
}
int main()
{
	scanf("%d", &n);
	for (int i = 1; i < n; i++)
	{
		int u, v;
		scanf("%d%d", &u, &v);
		add_edge(u, v), add_edge(v, u);
	}
	
	dfs(1, -1);
	for (int i = 1; i <= n; i++)
		add(i, 1);
	int q;
	scanf("%d", &q);
	while(q--)
	{
		getchar();
		char op = getchar();
		int u;
		scanf("%d", &u);
		if (op == 'Q')
		{
			int ans = query(tout[u]) - query(tin[u] - 1);
			printf("%d\n", ans);
		}
		else
		{
			int t = query(tin[u]) - query(tin[u] - 1);
			if (t == 1)
				add(tin[u], -1);
			else
				add(tin[u], 1);
		}
	}
	return 0;
}