Language: C++

#include <cstdio>
#include <vector>
#include <set>
#include <map>
#include <algorithm>
#include <iostream>
#include <string>
#define  debug	0
#define  MAXN  512
using namespace std;
int N;
map<string,bool> hash;
int main()
{				
#if debug 
freopen("data.txt","r",stdin);
#endif
	scanf("%d",&N);
	for(int i=0;i<N;i++) 
	{	string number;
		cin>>number;
		if(hash.find(number)==hash.end())
		{
			hash[number]=false;
		}
		else hash[number]=!hash[number];
	}
	int cnt=0;
	for(map<string,bool>::iterator i=hash.begin();i!=hash.end();i++)
	{
		if(i->second)cnt++;
	}
	printf("%d\n",cnt);
}


Compiler output:
a.cc: In function 'int main()':
a.cc:22:20: error: reference to 'hash' is ambiguous
   22 |                 if(hash.find(number)==hash.end())
      |                    ^~~~
In file included from /usr/include/c++/14/bits/stl_bvector.h:65,
                 from /usr/include/c++/14/vector:67,
                 from a.cc:2:
/usr/include/c++/14/bits/functional_hash.h:59:12: note: candidates are: 'template<class _Tp> struct std::hash'
   59 |     struct hash;
      |            ^~~~
a.cc:12:18: note:                 'std::map<std::__cxx11::basic_string<char>, bool> hash'
   12 | map<string,bool> hash;
      |                  ^~~~
a.cc:22:39: error: reference to 'hash' is ambiguous
   22 |                 if(hash.find(number)==hash.end())
      |                                       ^~~~
/usr/include/c++/14/bits/functional_hash.h:59:12: note: candidates are: 'template<class _Tp> struct std::hash'
   59 |     struct hash;
      |            ^~~~
a.cc:12:18: note:                 'std::map<std::__cxx11::basic_string<char>, bool> hash'
   12 | map<string,bool> hash;
      |                  ^~~~
a.cc:24:25: error: reference to 'hash' is ambiguous
   24 |                         hash[number]=false;
      |                         ^~~~
/usr/include/c++/14/bits/functional_hash.h:59:12: note: candidates are: 'template<class _Tp> struct std::hash'
   59 |     struct hash;
      |            ^~~~
a.cc:12:18: note:                 'std::map<std::__cxx11::basic_string<char>, bool> hash'
   12 | map<string,bool> hash;
      |                  ^~~~
a.cc:26:22: error: reference to 'hash' is ambiguous
   26 |                 else hash[number]=!hash[number];
      |                      ^~~~
/usr/include/c++/14/bits/functional_hash.h:59:12: note: candidates are: 'template<class _Tp> struct std::hash'
   59 |     struct hash;
      |            ^~~~
a.cc:12:18: note:                 'std::map<std::__cxx11::basic_string<char>, bool> hash'
   12 | map<string,bool> hash;
      |                  ^~~~
a.cc:26:36: error: reference to 'hash' is ambiguous
   26 |                 else hash[number]=!hash[number];
      |                                    ^~~~
/usr/include/c++/14/bits/functional_hash.h:59:12: note: candidates are: 'template<class _Tp> struct std::hash'
   59 |     struct hash;
      |            ^~~~
a.cc:12:18: note:                 'std::map<std::__cxx11::basic_string<char>, bool> hash'
   12 | map<string,bool> hash;
      |                  ^~~~
a.cc:29:42: error: reference to 'hash' is ambiguous
   29 |         for(map<string,bool>::iterator i=hash.begin();i!=hash.end();i++)
      |                                          ^~~~
/usr/include/c++/14/bits/functional_hash.h:59:12: note: candidates are: 'template<class _Tp> struct std::hash'
   59 |     struct hash;
      |            ^~~~
a.cc:12:18: note:                 'std::map<std::__cxx11::basic_string<char>, bool> hash'
   12 | map<string,bool> hash;
      |                  ^~~~
a.cc:29:58: error: reference to 'hash' is ambiguous
   29 |         for(map<string,bool>::iterator i=hash.begin();i!=hash.end();i++)
      |                                                          ^~~~
/usr/include/c++/14/bits/functional_hash.h:59:12: note: candidates are: 'template<class _Tp> struct std::hash'
   59 |     struct hash;
      |            ^~~~
a.cc:12:18: note:                 'std::map<std::__cxx11::basic_string<char>, bool> hash'
   12 | map<string,bool> hash;
      |                  ^~~~