Language: C++

#include <bits/stdc++.h>
using namespace std;
bool e[2000][2000];
int main() {
  cin.tie(0); ios::sync_with_stdio(false);
  int n, k; cin >> n >> k;
  int a[n - 1], b[n - 1];
  for (int i = 0; i < n - 1; i++) {
    cin >> a[i] >> b[i];
    a[i]--; b[i]--;
    e[a[i]][b[i]] = e[b[i]][a[i]] = 1;
  }
  int res = 0;
  if (k % 2 == 0) {
    k /= 2;
    int v;
    int memo[n];
    for (int i = 0; i < n; i++) {
      memset(memo, -1, sizeof(memo));
      queue<int> q;
      memo[i] = 0, q.push(i);
      while (!q.empty()) {
        v = q.front(); q.pop();
        for (int j = 0; j < n; j++) {
          if (e[v][j] and memo[j] == -1) {
            memo[j] = memo[v] + 1;
            q.push(j);
          }
        }
      }
      sort(memo, memo + n);
      res = max(res, upper_bound(memo, memo + n, k) - lower_bound(memo, memo + n, 0));
    }
  } else {
    k /= 2;
    int v;
    int memo[n];
    for (int i = 0; i < n - 1; i++) {
      memset(memo, -1, sizeof(memo));
      queue<int> q;
      memo[a[i]] = memo[b[i]] = 0;
      q.push(a[i]); q.push(b[i]);
      while (!q.empty()) {
        v = q.front(); q.pop();
        for (int j = 0; j < n; j++) {
          if (e[v][j] and memo[j] == -1) {
            memo[j] = memo[v] + 1;
            q.push(j);
          }
        }
      }
      sort(memo, memo + n);
      res = max(res, upper_bound(memo, memo + n, k) - lower_bound(memo, memo + n, 0));
    }
  }
  cout << n - res << "\n";
  return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:32:16: error: no matching function for call to 'max(int&, long int)'
   32 |       res = max(res, upper_bound(memo, memo + n, k) - lower_bound(memo, memo + n, 0));
      |             ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/14/algorithm:60,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_algobase.h:257:5: note: candidate: 'template<class _Tp> constexpr const _Tp& std::max(const _Tp&, const _Tp&)'
  257 |     max(const _Tp& __a, const _Tp& __b)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:257:5: note:   template argument deduction/substitution failed:
a.cc:32:16: note:   deduced conflicting types for parameter 'const _Tp' ('int' and 'long int')
   32 |       res = max(res, upper_bound(memo, memo + n, k) - lower_bound(memo, memo + n, 0));
      |             ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note: candidate: 'template<class _Tp, class _Compare> constexpr const _Tp& std::max(const _Tp&, const _Tp&, _Compare)'
  303 |     max(const _Tp& __a, const _Tp& __b, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note:   candidate expects 3 arguments, 2 provided
In file included from /usr/include/c++/14/algorithm:61:
/usr/include/c++/14/bits/stl_algo.h:5706:5: note: candidate: 'template<class _Tp> constexpr _Tp std::max(initializer_list<_Tp>)'
 5706 |     max(initializer_list<_Tp> __l)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5706:5: note:   candidate expects 1 argument, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5716:5: note: candidate: 'template<class _Tp, class _Compare> constexpr _Tp std::max(initializer_list<_Tp>, _Compare)'
 5716 |     max(initializer_list<_Tp> __l, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5716:5: note:   template argument deduction/substitution failed:
a.cc:32:16: note:   mismatched types 'std::initializer_list<_Tp>' and 'int'
   32 |       res = max(res, upper_bound(memo, memo + n, k) - lower_bound(memo, memo + n, 0));
      |             ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
a.cc:53:16: error: no matching function for call to 'max(int&, long int)'
   53 |       res = max(res, upper_bound(memo, memo + n, k) - lower_bound(memo, memo + n, 0));
      |             ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:257:5: note: candidate: 'template<class _Tp> constexpr const _Tp& std::max(const _Tp&, const _Tp&)'
  257 |     max(const _Tp& __a, const _Tp& __b)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:257:5: note:   template argument deduction/substitution failed:
a.cc:53:16: note:   deduced conflicting types for parameter 'const _Tp' ('int' and 'long int')
   53 |       res = max(res, upper_bound(memo, memo + n, k) - lower_bound(memo, memo + n, 0));
      |             ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note: candidate: 'template<class _Tp, class _Compare> constexpr const _Tp& std::max(const _Tp&, const _Tp&, _Compare)'
  303 |     max(const _Tp& __a, const _Tp& __b, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note:   candidate expects 3 arguments, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5706:5: note: candidate: 'template<class _Tp> constexpr _Tp std::max(initializer_list<_Tp>)'
 5706 |     max(initializer_list<_Tp> __l)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5706:5: note:   candidate expects 1 argument, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5716:5: note: candidate: 'template<class _Tp, class _Compare> constexpr _Tp std::max(initializer_list<_Tp>, _Compare)'
 5716 |     max(initializer_list<_Tp> __l, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5716:5: note:   template argument deduction/substitution failed:
a.cc:53:16: note:   mismatched types 'std::initializer_list<_Tp>' and 'int'
   53 |       res = max(res, upper_bound(memo, memo + n, k) - lower_bound(memo, memo + n, 0));
      |             ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~