Language: C++

#ifdef LOCAL111
	#define _GLIBCXX_DEBUG
#else
	#define NDEBUG
#endif
#include <bits/stdc++.h>
const int INF = 1e9;
using namespace std;
template<typename T, typename U> ostream& operator<< (ostream& os, const pair<T,U>& p) { cout << '(' << p.first << ' ' << p.second << ')'; return os; }

//library
typedef long long cost_t;

class Edge {
public:
	int to;
	cost_t cost;
	
	Edge(){
	}

	Edge(int x,cost_t y){
		to = x;
		cost = y;
	}

	bool operator< (const Edge& x) const {
		if(cost != x.cost) return cost < x.cost;
		return to < x.to;
	}

	bool operator> (const Edge& x) const {
		if(cost != x.cost) return cost > x.cost;
		return to > x.to;
	}
};

class Graph {
private:
	//const long long int INF = (long long)1e18;
	vector<vector<Edge> > v; 
	int n;
public:
	Graph(int x){
		n = x;
		v = vector<vector<Edge> >(x);
	}

	vector<Edge>& operator[](int x){
		return v[x];
	}

	const vector<Edge>& operator[](int x) const {
		return v[x];
	}

	int size() const {
		return n;
	}

	void add_edge(int from, Edge e){
		v[from].push_back(e);
	}

	void add_edge(int from, int to, cost_t cost){
		add_edge(from,Edge(to,cost));
	}

	void add_uedge(int from, int to, cost_t cost){
		add_edge(from,to,cost);
		add_edge(to,from,cost);
	}
};

vector<cost_t> dijkstra(int from, const Graph& v)
{
	vector<cost_t> dist(v.size(),INF);
	priority_queue<Edge,vector<Edge>,greater<Edge>> que;
	que.push(Edge(from,0));
	while(!que.empty()){
		Edge e = que.top();
		que.pop();
		if(dist[e.to] == INF){
			dist[e.to] = e.cost;
			for(auto to : v[e.to]){
				if(dist[to.to] == INF)
					que.push(Edge(to.to, e.cost+to.cost));
			}
		}
	}
	return dist;
}

vector<cost_t> bellmanford(int from, const Graph& g)
{
	vector<cost_t> res(g.size(),INF);
	res[from] = 0;
	bool conf = true;
	int cnt = 0;
	while(conf){
		conf = false;
		for(int i = 0; i < g.size(); i++){
			if(res[i] != INF)
			for(const auto& e : g[i]){
				if(res[e.to] > res[i]+e.cost){
					conf = true;
					res[e.to] = res[i]+e.cost;
				}
			}
		}
		if(cnt > g.size()+5) return vector<cost_t>();
		cnt++;
	}
	return res;
}

Graph prim(const Graph g)
{
	using T = tuple<cost_t, int, int>;
	priority_queue<T, vector<T>, greater<T>> qu;
	int n = g.size();
	assert(n != 0);
	vector<bool> added(n,false);
	qu.emplace(0,0,0);
	Graph res(n);
	while(!qu.empty()){
		int from, to;
		cost_t cost;
		tie(cost, from, to) = qu.top();
		qu.pop();
		if(!added[to]){
			added[to] = true;
			res.add_edge(from, to, cost);
			res.add_edge(to, from, cost);
			for(const auto &e : g[to]){
				if(!added[e.to]){
					qu.emplace(e.cost, to, e.to);
				}
			}
		}
	}
	return res;
}

vector<int> tree_getorder(const Graph &g, int root)
{
	vector<int> res;
	function<void(int p, int pre)> func = [&](int p, int pre){
		for(auto &e : g[p]){
			if(e.to != pre){
				func(e.to,p);
			}
		}
		res.push_back(p);
	};
	func(root,-1);
	return res;
}

vector<int> tree_getpar(const Graph &g, int root)
{
	vector<int> par(g.size(),root);
	function<void(int p, int pre)> func = [&](int p, int pre){
		par[p] = pre;
		for(auto &e : g[p]){
			if(e.to != pre){
				func(e.to,p);
			}
		}
	};
	func(root,root);
	return par;
}


//未検証
vector<int> toposort(const Graph &g, int start)
{
	int n = g.size();
	vector<int> res;
	res.reserve(n);
	vector<bool> used(n,false);
	function<void(int)> rec = [&](int p){
		if(used[p]) return;
		used[p] = true;
		for(auto&& e : g[p]) {
			rec(e.to);
		}
		res.push_back(p);
	};
	rec(start);
	return res;
}

//liblary

void vizGraph(const Graph &g, bool with_dir = false, bool with_cap = false){
	ofstream ofs("./out.dot");
	if(with_dir) ofs << "graph graph_name {" << endl;
	else ofs << "digraph graph_name {" << endl;
	for(int i = 0; i < (int)g.size(); i++){
		if (!g[i].size())
			continue;
		for(const auto &e : g[i]){
			if(with_dir){
				if(e.to > i) ofs << "    \"" << i << "\" -- \"" << e.to << '"'; 
			}else ofs << "    \"" << i << "\" -> \"" << e.to << '"'; 
			
			if (with_cap) {
				ofs << " [ label = \"" << (e.cost  == INF ? "inf" : to_string(e.cost)) << "\"];"; 
			}
			if(!with_dir or e.to > i)ofs << endl;
		}
	}
	ofs << "}" << endl;
	ofs.close();
	system("dot -T png out.dot > sample.png");	
}

#define endl '\n'
#define ALL(a)  (a).begin(),(a).end()
#define SZ(a) int((a).size())
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n)  FOR(i,0,n)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)
#ifdef LOCAL111
	#define DEBUG(x) cout<<#x<<": "<<(x)<<endl
	template<typename T> void dpite(T a, T b){ for(T ite = a; ite != b; ite++) cout << (ite == a ? "" : " ") << *ite; cout << endl;}
#else
	#define DEBUG(x) true
	template<typename T> void dpite(T a, T b){ return; }
#endif
#define F first
#define S second
#define SNP string::npos
#define WRC(hoge) cout << "Case #" << (hoge)+1 << ": "
template<typename T> void pite(T a, T b){ for(T ite = a; ite != b; ite++) cout << (ite == a ? "" : " ") << *ite; cout << endl;}
template<typename T> bool chmax(T& a, T b){if(a < b){a = b; return true;} return false;}
template<typename T> bool chmin(T& a, T b){if(a > b){a = b; return true;} return false;}

typedef long long int LL;
typedef unsigned long long ULL;
typedef pair<int,int> P;
typedef pair<LL,LL> LP;

tuple<cost_t,int,int> getTreeDiameter(const Graph &g){
	using P = pair<cost_t,int>;
	
	function<P(int,int)> dfs = [&](int p, int par) -> P{
		P res = {0,p};
		for(auto&& e : g[p]) {
			if(e.to == par or erased[e.to]) continue;
			auto v = dfs(e.to,p);
			v.first += e.cost;
			res = max(res,v);
		}
		return res;
	};
	
	int r = -100;
	REP(i,SZ(erased)) if(!erased[i]){
		r = i;	
		break;
	}
	auto ap1 = dfs(0,-1);
	auto ap2 = dfs(ap1.second,-1);
	return make_tuple(ap2.first,ap2.second,ap1.second);
}

pair<int,int> getTreeCenter(const Graph& g){
	cost_t di;
	int x, y;
	tie(di, x, y) = getTreeDiameter(g, erased);
	DEBUG(di);
	pair<int,int> res(-1,-1);
	cost_t mi;
	function<cost_t(int,int)> rec 
	 = [&](int p, int par) -> cost_t{
		if(p == y){
			return 0;
		}
		cost_t ress = -1;
		for(auto&& e : g[p]) if(e.to != par and !erased[e.to]){
			cost_t v = rec(e.to,p);
			if(v != -1){
				v += e.cost;
				ress = v;
				v = max(v, di-(v));
				if(mi > v){
					mi = v;
					res = {p,-1};
				}else if(mi == v){
					res.second = p;
				}
			}
		}
		return ress;
	};
	rec(x,-1);
	return res;
}

void ios_init(){
	//cout.setf(ios::fixed);
	//cout.precision(12);
#ifdef LOCAL111
	return;
#endif
	ios::sync_with_stdio(false); cin.tie(0);	
}

int main()
{
	ios_init();
	int n, k;
	while(cin >> n >> k) {
		Graph g(n);
		REP(i,n-1){
			int a,b;
			cin >> a >> b;
			a--; b--;
			g.add_uedge(a,b,1);
		}
		int di;
		tie(di,ignore, ignore) = getTreeDiameter(g);
		int ans = 0;
		int r = (di+1)/2-k;
		while(true){
			P c;
			c = getTreeCenter(g);
			vector<bool> used(n,false);
			function<void(int,int)> dfs = [&](int p, int d){
				used[p] = true;
				if(d >= r){
					ans++;
				}
				for(auto&& e : g[p]) if(!used[e.to]){
					dfs(e.to,d+1);
				}
			};
			dfs(c.F,0);
			fill(ALL(used),false);
			if(c.S != -1) dfs(c.S,0);
		}
		cout << ans << endl;
	}
	return 0;
}


Compiler output:
a.cc: In lambda function:
a.cc:253:43: error: 'erased' was not declared in this scope
  253 |                         if(e.to == par or erased[e.to]) continue;
      |                                           ^~~~~~
a.cc: In function 'std::tuple<long long int, int, int> getTreeDiameter(const Graph&)':
a.cc:262:18: error: 'erased' was not declared in this scope
  262 |         REP(i,SZ(erased)) if(!erased[i]){
      |                  ^~~~~~
a.cc:223:37: note: in definition of macro 'FOR'
  223 | #define FOR(i,a,b) for(int i=(a);i<(b);++i)
      |                                     ^
a.cc:262:9: note: in expansion of macro 'REP'
  262 |         REP(i,SZ(erased)) if(!erased[i]){
      |         ^~~
a.cc:262:15: note: in expansion of macro 'SZ'
  262 |         REP(i,SZ(erased)) if(!erased[i]){
      |               ^~
a.cc: In function 'std::pair<int, int> getTreeCenter(const Graph&)':
a.cc:274:44: error: 'erased' was not declared in this scope
  274 |         tie(di, x, y) = getTreeDiameter(g, erased);
      |                                            ^~~~~~