Language: C++

#include <iostream>
#include <algorithm>
#include <cstring>

using namespace std;

int N;
int x[24], y[24], r[24], c[24];
int on[24];

#define SQ(x) ((x)*(x))
inline bool isIntersect(int i, int j) {
  return SQ(x[j]-x[i]) + SQ(y[j]-y[i]) < SQ(r[j]+r[i]);
}

inline bool isValid(int i, int S) {
  for(int j=0; j<i; j++) {
    if((on[i]>>j & 1) && !(S>>j & 1)) return false;
  }
  return true;
}

char memo[1<<24];
int dfs(int S, const int sum) {
  char& ret = memo[S];
  if(ret != -1) return ret;
  ret = sum;
  for(int i=0; i<N; i++) {
    if(S>>i & 1) continue;
    if(!isValid(i, S)) continue;
    for(int j=0; j<N; j++) {
      if(i == j) continue;
      if(c[i]!=c[j]) continue;
      if(S>>j & 1) continue;
      if(!isValid(j, S)) continue;
      ret = max(ret, dfs(S+(1<<i)+(1<<j), sum+2));
    }
  }
  
  return ret;
}

int main() {
  
  while(cin >> N && N) {
    for(int i=0; i<N; i++) {
      cin >> x[i] >> y[i] >> r[i] >> c[i];
      on[i] = 0;
      for(int j=0; j<i; j++) {
        if(isIntersect(i, j)) on[i] += 1<<j;
      }
    }
    memset(memo, -1, sizeof memo);
    cout << dfs(0, 0) << endl;
  }
  
  return 0;
}

Compiler output:
a.cc: In function 'int dfs(int, int)':
a.cc:36:16: error: no matching function for call to 'max(char&, int)'
   36 |       ret = max(ret, dfs(S+(1<<i)+(1<<j), sum+2));
      |             ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/14/string:51,
                 from /usr/include/c++/14/bits/locale_classes.h:40,
                 from /usr/include/c++/14/bits/ios_base.h:41,
                 from /usr/include/c++/14/ios:44,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 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:36:16: note:   deduced conflicting types for parameter 'const _Tp' ('char' and 'int')
   36 |       ret = max(ret, dfs(S+(1<<i)+(1<<j), sum+2));
      |             ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/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,
                 from a.cc:2:
/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:36:16: note:   mismatched types 'std::initializer_list<_Tp>' and 'char'
   36 |       ret = max(ret, dfs(S+(1<<i)+(1<<j), sum+2));
      |             ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~