Language: C++

#include <bits/stdc++.h>

#define SORT(v, n) sort(v, v+n);
#define VSORT(v) sort(v.begin(), v.end());
#define INF 999999999
#define size_t unsigned long long
#define ll long long
#define rep(i,a) for(int i=0;i<(a);i++)
#define repr(i,a) for(int i=(int)(a)-1;i>=0;i--)
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define FORR(i,a,b) for(int i=(int)(b)-1;i>=a;i--)
#define ALL(a) a.begin(), a.end()
using namespace std;
int si() { int x; scanf("%d", &x); return x; }
long long sl() { long long x; scanf("%lld", &x); return x; }
string ss() { string x; cin >> x; return x; }
void pi(int x) { printf("%d ", x); }
void pl(long long x) { printf("%lld ", x); }
void pd(double x) { printf("%.15f ", x); }
void ps(const string &s) { printf("%s ", s.c_str()); }
void br() { putchar('\n'); }

const int MOD = 1e9 + 7;

struct mint {
    int n;
    mint(int n_ = 0) : n(n_) {}
};

mint operator+(mint a, mint b) { a.n += b.n; if (a.n >= MOD) a.n -= MOD; return a; }
mint operator-(mint a, mint b) { a.n -= b.n; if (a.n < 0) a.n += MOD; return a; }
mint operator*(mint a, mint b) { return (long long)a.n * b.n % MOD; }
mint &operator+=(mint &a, mint b) { return a = a + b; }
mint &operator-=(mint &a, mint b) { return a = a - b; }
mint &operator*=(mint &a, mint b) { return a = a * b; }

typedef pair<int, int> P;

const int N = 1e6+5;
string s;
int n,m;
map<char, int> ma;
map<char, int>::iterator ite;

int main () {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cin >> n;
  rep(i,n) {
    cin >> s;
    ma[s]++;
  }
  cin >> m;
  rep(i,m) {
    cin >> s;
    ma[s]--;
  }
  int result = 0;
  for(ite = ma.begin(); ite != ma.end(); ++ite) result = max(result, ite->second);
  cout << result << endl;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:51:7: error: no match for 'operator[]' (operand types are 'std::map<char, int>' and 'std::string' {aka 'std::__cxx11::basic_string<char>'})
   51 |     ma[s]++;
      |       ^
In file included from /usr/include/c++/14/map:63,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:152,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_map.h:504:7: note: candidate: 'std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](const key_type&) [with _Key = char; _Tp = int; _Compare = std::less<char>; _Alloc = std::allocator<std::pair<const char, int> >; mapped_type = int; key_type = char]'
  504 |       operator[](const key_type& __k)
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_map.h:504:34: note:   no known conversion for argument 1 from 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'const std::map<char, int>::key_type&' {aka 'const char&'}
  504 |       operator[](const key_type& __k)
      |                  ~~~~~~~~~~~~~~~~^~~
/usr/include/c++/14/bits/stl_map.h:524:7: note: candidate: 'std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](key_type&&) [with _Key = char; _Tp = int; _Compare = std::less<char>; _Alloc = std::allocator<std::pair<const char, int> >; mapped_type = int; key_type = char]'
  524 |       operator[](key_type&& __k)
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_map.h:524:29: note:   no known conversion for argument 1 from 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'std::map<char, int>::key_type&&' {aka 'char&&'}
  524 |       operator[](key_type&& __k)
      |                  ~~~~~~~~~~~^~~
a.cc:56:7: error: no match for 'operator[]' (operand types are 'std::map<char, int>' and 'std::string' {aka 'std::__cxx11::basic_string<char>'})
   56 |     ma[s]--;
      |       ^
/usr/include/c++/14/bits/stl_map.h:504:7: note: candidate: 'std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](const key_type&) [with _Key = char; _Tp = int; _Compare = std::less<char>; _Alloc = std::allocator<std::pair<const char, int> >; mapped_type = int; key_type = char]'
  504 |       operator[](const key_type& __k)
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_map.h:504:34: note:   no known conversion for argument 1 from 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'const std::map<char, int>::key_type&' {aka 'const char&'}
  504 |       operator[](const key_type& __k)
      |                  ~~~~~~~~~~~~~~~~^~~
/usr/include/c++/14/bits/stl_map.h:524:7: note: candidate: 'std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](key_type&&) [with _Key = char; _Tp = int; _Compare = std::less<char>; _Alloc = std::allocator<std::pair<const char, int> >; mapped_type = int; key_type = char]'
  524 |       operator[](key_type&& __k)
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_map.h:524:29: note:   no known conversion for argument 1 from 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'std::map<char, int>::key_type&&' {aka 'char&&'}
  524 |       operator[](key_type&& __k)
      |                  ~~~~~~~~~~~^~~