Language: C++

#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<algorithm>
#define pb push_back
#define all(c) c.begin(),c.end()
#define uni(c) c.erase(unique(all(c)),c.end())
using namespace std;
typedef __int64 ll;
int main(){
	string s;
	while(cin>>s){
		map<char,ll> m;
		for(ll i=0;i<s.size();i++){
			m[s[i]]++;
		}
		
		ll odd=0,even=0;
		map<char,ll>::iterator ite=m.begin();
		vector<ll> v;
		map<ll,ll> d;
		for(ite=m.begin();ite!=m.end();ite++){
			if(ite->second%2==1){
				odd++;
				if(ite->second>=3){
					v.pb((ite->second-1)/2);
					for(int j=2;j<=(ite->second-1)/2;j++){
						d[j]++;
					}
				}
			}else{
				even++;
				v.pb((ite->second)/2);
				for(ll j=2;j<=(ite->second)/2;j++){
					d[j]++;
				}
			}
		}
		if(odd>1){
			cout<<0<<endl;
			continue;
		}
		ll ans=1;
		for(ll i=1;i<=s.size()/2;i++){
			//cout<<ans<<endl;
			if(d[i]){
				d[i]--;
			}else
			ans*=i;
		}
		map<ll,ll>::iterator it=d.begin();
		for(it=d.begin();it!=d.end();it++){
			for(int l=0;l<it->second;l++){
				for(ll k=1;k<=it->first;k++){
					ans/=k;
				}
			}
		}
		
		cout<<ans<<endl;
	}
	return 0;
}

Compiler output:
a.cc:11:9: error: '__int64' does not name a type; did you mean '__int64_t'?
   11 | typedef __int64 ll;
      |         ^~~~~~~
      |         __int64_t
a.cc: In function 'int main()':
a.cc:15:26: error: 'll' was not declared in this scope; did you mean 'all'?
   15 |                 map<char,ll> m;
      |                          ^~
      |                          all
a.cc:15:28: error: template argument 2 is invalid
   15 |                 map<char,ll> m;
      |                            ^
a.cc:15:28: error: template argument 4 is invalid
a.cc:16:23: error: expected ';' before 'i'
   16 |                 for(ll i=0;i<s.size();i++){
      |                       ^~
      |                       ;
a.cc:16:28: error: 'i' was not declared in this scope
   16 |                 for(ll i=0;i<s.size();i++){
      |                            ^
a.cc:20:19: error: expected ';' before 'odd'
   20 |                 ll odd=0,even=0;
      |                   ^~~~
      |                   ;
a.cc:21:28: error: template argument 4 is invalid
   21 |                 map<char,ll>::iterator ite=m.begin();
      |                            ^
a.cc:21:40: error: expected initializer before 'ite'
   21 |                 map<char,ll>::iterator ite=m.begin();
      |                                        ^~~
a.cc:22:26: error: template argument 2 is invalid
   22 |                 vector<ll> v;
      |                          ^
a.cc:23:26: error: template argument 3 is invalid
   23 |                 map<ll,ll> d;
      |                          ^
a.cc:23:26: error: template argument 4 is invalid
a.cc:24:21: error: 'ite' was not declared in this scope
   24 |                 for(ite=m.begin();ite!=m.end();ite++){
      |                     ^~~
a.cc:24:27: error: request for member 'begin' in 'm', which is of non-class type 'int'
   24 |                 for(ite=m.begin();ite!=m.end();ite++){
      |                           ^~~~~
a.cc:24:42: error: request for member 'end' in 'm', which is of non-class type 'int'
   24 |                 for(ite=m.begin();ite!=m.end();ite++){
      |                                          ^~~
a.cc:26:33: error: 'odd' was not declared in this scope
   26 |                                 odd++;
      |                                 ^~~
a.cc:7:12: error: request for member 'push_back' in 'v', which is of non-class type 'int'
    7 | #define pb push_back
      |            ^~~~~~~~~
a.cc:28:43: note: in expansion of macro 'pb'
   28 |                                         v.pb((ite->second-1)/2);
      |                                           ^~
a.cc:30:50: error: invalid types 'int[int]' for array subscript
   30 |                                                 d[j]++;
      |                                                  ^
a.cc:34:33: error: 'even' was not declared in this scope
   34 |                                 even++;
      |                                 ^~~~
a.cc:7:12: error: request for member 'push_back' in 'v', which is of non-class type 'int'
    7 | #define pb push_back
      |            ^~~~~~~~~
a.cc:35:35: note: in expansion of macro 'pb'
   35 |                                 v.pb((ite->second)/2);
      |                                   ^~
a.cc:36:39: error: expected ';' before 'j'
   36 |                                 for(ll j=2;j<=(ite->second)/2;j++){
      |                                       ^~
      |                                       ;
a.cc:36:44: error: 'j' was not declared in this scope
   36 |                                 for(ll j=2;j<=(ite->second)/2;j++){
      |                                            ^
a.cc:41:20: error: 'odd' was not declared in this scope
   41 |                 if(odd>1){
      |                    ^~~
a.cc:45:19: error: expected ';' before 'ans'
   45 |                 ll ans=1;
      |                   ^~~~
      |                   ;
a.cc:46:23: error: expected ';' before 'i'
   46 |                 for(ll i=1;i<=s.size()/2;i++){
      |                       ^~
      |                       ;
a.cc:46:28: error: 'i' was not declared in this scope
   46 |                 for(ll i=1;i<=s.size()/2;i++){
      |                            ^
a.cc:51:25: error: 'ans' was not declared in this scope; did you mean 'abs'?
   51 |                         ans*=i;
      |                         ^~~
      |                         abs
a.cc:53:26: error: template argument 3 is invalid
   53 |                 map<ll,ll>::iterator it=d.begin();
      |                          ^
a.cc:53:26: error: template argument 4 is invalid
a.cc:53:38: error: expected initializer before 'it'
   53 |                 map<ll,ll>::iterator it=d.begin();
      |                                      ^~
a.cc:54:21: error: 'it' was not declared in this scope; did you mean 'int'?
   54 |                 for(it=d.begin();it!=d.end();it++){
      |                     ^~
      |                     int
a.cc:54:26: error: request for member 'begin' in 'd', which is of non-class type 'int'
   54 |                 for(it=d.begin();it!=d.end();it++){
      |                          ^~~~~
a.cc:54:40: error: request for member 'end' in 'd', which is of non-class type 'int'
   54 |                 for(it=d.begin();it!=d.end();it++){
      |                                        ^~~
a.cc:56:39: error: expected ';' before 'k'
   56 |                                 for(ll k=1;k<=it->first;k++){
      |                                       ^~
      |                                       ;
a.cc:56:44: error: 'k' was not declared in this scope
   56 |                                 for(ll k=1;k<=it->first;k++){
      |                                            ^
a.cc:57:41: error: 'ans' was not declared in this scope; did you mean 'abs'?
   57 |                                         ans/=k;
      |                                         ^~~
      |                                         abs
a.cc:62:23: error: 'ans' was not declared in this scope; did you mean 'abs'?
   62 |                 cout<<ans<<endl;
      |                       ^~~
      |                       abs