Language: C++

#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <iterator>
#include <unordered_map>
#include <unordered_set>
#include <tuple> 
#include <memory>
#include <random>
#include <iterator>

using namespace std;

//ユニークな要素数
template <typename T>
unsigned long long UniqueElementNum(const vector<T>& data)
{
	auto copy = data;

	sort(begin(copy), end(copy));
	copy.erase(unique(begin(copy), end(copy)), end(copy));

	return copy.size();

	//set<unsigned long long>(begin(copy), end(copy)).size();
}

//最小公倍数
long long gcd(long long a, long long b)
{
	long long c;

	if (a < b) {
		a += b; b = a - b; a -= b;
	}

	while (b != 0) {
		c = a % b;
		a = b;
		b = c;
	}

	return a;
}

//要素数Nと各要素をコンテナに格納
//#TODO いろんなコンテナに対応
template <typename ElementNum, typename Container>
void InputNumAndElement(ElementNum& num, Container& container)
{
	cin >> num;

	container.resize(num);
	for (auto& d : container) {
		cin >> d;
	}
}

//コンテナの内容をstreamへ出力
//今はてきとーにcoutへ改行しながら　果たしてこの書き方は便利なのか…？
//#TODO 引数増やしたりオーバーロード増やしたり
template <typename Container>
void ShowContainer(const Container& container)
{
	ostream_iterator<string> outItr(cout, "\n");
	copy(container.begin(), container.end(), outItr);
	cout << endl;
}

int main() {
	unsigned long long N, M;
	vector<string> bludCardList, redCardList;
	InputNumAndElement(N, bludCardList);
	InputNumAndElement(M, redCardList);


	//ShowContainer(bludCardList);
	//ShowContainer(redCardList);

	vector<string> blueCopy = bludCardList;
	sort(begin(blueCopy), end(blueCopy));
	blueCopy.erase(unique(begin(blueCopy), end(blueCopy)), end(blueCopy));

	long long maxValue = 0;
	for (const auto& u : blueCopy) {
		auto value = count(begin(bludCardList), end(bludCardList), u) - count(begin(redCardList), end(redCardList), u);
		maxValue = std::max(value, maxValue);
	}

	cout << maxValue;

	return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:106:36: error: no matching function for call to 'max(long int&, long long int&)'
  106 |                 maxValue = std::max(value, maxValue);
      |                            ~~~~~~~~^~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/14/vector:62,
                 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:106:36: note:   deduced conflicting types for parameter 'const _Tp' ('long int' and 'long long int')
  106 |                 maxValue = std::max(value, maxValue);
      |                            ~~~~~~~~^~~~~~~~~~~~~~~~~
/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:9:
/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:106:36: note:   mismatched types 'std::initializer_list<_Tp>' and 'long int'
  106 |                 maxValue = std::max(value, maxValue);
      |                            ~~~~~~~~^~~~~~~~~~~~~~~~~