Language: C++

#include <vector>                                                                                                                                                                                           
#include <numeric>                                                                                                                                                                                          
#include <cstdlib>                                                                                                                                                                                          
#include <queue>                                                                                                                                                                                            
#include <stack>                                                                                                                                                                                            
using namespace std;                                                                                                                                                                                        
                                                                                                                                                                                                            
typedef long long ll;                                                                                                                                                                                       
#define pb push_back                                                                                                                                                                                        
                                                                                                                                                                                                            
#define rep(i, n) for (int i=0;i<(n);++i)                                                                                                                                                                   
#define rep2(i, s, n) for (int i=s;i<(n);++i)                                                                                                                                                               
#define INF (1e9)                                                                                                                                                                                           
                                                                                                                                                                                                            
int main()                                                                                                                                                                                                  
{                                                                                                                                                                                                           
    int h,w; cin>>h>>w;                                                                                                                                                                                     
                                                                                                                                                                                                            
    vector<int> d(26, 0);                                                                                                                                                                                   
                                                                                                                                                                                                            
    rep(i,h) {                                                                                                                                                                                              
        string s; cin >> s;                                                                                                                                                                                 
                                                                                                                                                                                                            
        rep(k,s.length()) d[s[k]-97]++;                                                                                                                                                                     
    }                                                                                                                                                                                                       
                                                                                                                                                                                                            
                                                                                                                                                                                                            
    bool ans = true;                                                                                                                                                                                        
    if (h%2==0 || w%2==0) {                                                                                                                                                                                 
        for(auto& e:d) if (e != 0 && e%2 != 0) ans = false;                                                                                                                                                 
    } else {                                                                                                                                                                                                
        int odd_cnt = 0;                                                                                                                                                                                    
        for(auto& e:d) if (e != 0 && e%2 != 0) odd_cnt++;                                                                                                                                                   
        if (odd_cnt != 1) ans = false;                                                                                                                                                                      
    }                                                                                                                                                                                                       
                                                                                                                                                                                                            
    int kind = 0;                                                                                                                                                                                           
    int m = max(h,w);                                                                                                                                                                                       
    for(auto& e:d) if (e!=0) kind++;                                                                                                                                                                        
    if (m %2==0 && kind >= m) {ans = false;}                                                                                                                                                                
    else if(m%2 != 0 && kind-1 >= m) {ans = false;}                                                                                                                                                         
                                                                                                                                                                                                            
    if(ans) cout << "Yes" << endl;                                                                                                                                                                          
    else cout << "No" << endl;                                                                                                                                                                              
                                                                                                                                                                                                            
}   

Compiler output:
a.cc: In function 'int main()':
a.cc:17:14: error: 'cin' was not declared in this scope
   17 |     int h,w; cin>>h>>w;
      |              ^~~
a.cc:6:1: note: 'std::cin' is defined in header '<iostream>'; this is probably fixable by adding '#include <iostream>'
    5 | #include <stack>
  +++ |+#include <iostream>
    6 | using namespace std;
a.cc:22:9: error: 'string' was not declared in this scope
   22 |         string s; cin >> s;
      |         ^~~~~~
a.cc:6:1: note: 'std::string' is defined in header '<string>'; this is probably fixable by adding '#include <string>'
    5 | #include <stack>
  +++ |+#include <string>
    6 | using namespace std;
a.cc:22:26: error: 's' was not declared in this scope
   22 |         string s; cin >> s;
      |                          ^
a.cc:43:13: error: 'cout' was not declared in this scope
   43 |     if(ans) cout << "Yes" << endl;
      |             ^~~~
a.cc:43:13: note: 'std::cout' is defined in header '<iostream>'; this is probably fixable by adding '#include <iostream>'
a.cc:43:30: error: 'endl' was not declared in this scope
   43 |     if(ans) cout << "Yes" << endl;
      |                              ^~~~
a.cc:6:1: note: 'std::endl' is defined in header '<ostream>'; this is probably fixable by adding '#include <ostream>'
    5 | #include <stack>
  +++ |+#include <ostream>
    6 | using namespace std;
a.cc:44:10: error: 'cout' was not declared in this scope
   44 |     else cout << "No" << endl;
      |          ^~~~
a.cc:44:10: note: 'std::cout' is defined in header '<iostream>'; this is probably fixable by adding '#include <iostream>'
a.cc:44:26: error: 'endl' was not declared in this scope
   44 |     else cout << "No" << endl;
      |                          ^~~~
a.cc:44:26: note: 'std::endl' is defined in header '<ostream>'; this is probably fixable by adding '#include <ostream>'