本题是无向图，建边要建双向
by Ke9_qux @ 2024-08-23 21:26:24
```cpp
g[u].push_back(v);
g[v].push_back(u);
```
by 奈芙蓮 @ 2024-08-23 21:26:36
```cpp
#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 10;
int n, d;
vector<int> g[N];
set<int> s;
int vis[N];
void dfs(int u, int fa, int step) {
vis[u] = 1;
if (step <= d) {
s.insert(u);
if (step == d) return ;
}
for (auto v : g[u]) {
if (!vis[v]) {
dfs(v, u, step + 1);
}
}
}
int main()
{
cin >> n >> d;
for (int i = 1; i < n; i++) {
int u, v;
cin >> u >> v;
g[u].push_back(v);
g[v].push_back(u);
}
dfs(1, 0, 0);
cout << s.size() - 1;
return 0;
}
```
by Perry6632 @ 2024-08-23 21:30:05
@[Ke9_qux](/user/678867) @[奈芙蓮](/user/1293516) 感谢两个红名dalao，已关
by topcsa @ 2024-09-02 21:10:22