Language: C++

#include <bits/stdc++.h>
#define for0(i, n) for(int i = 0; i < n; i++)
#define for1(i, n) for(int i = 1; i <= n; i++)
#define pb push_back
#define mp make_pair
#define all(v) v.begin(), v.end()
#define V vector<int>
#define VP vector<pair<int, int> >
#define FASTIO ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0)
using namespace std;
#ifdef _WIN32
#include <windows.h>
#define print(x) PRINT(x, #x)
template<typename T> inline const void PRINT(T VARIABLE, string NAME)
{
#ifndef ONLINE_JUDGE /// ONLINE_JUDGE IS DEFINED ON CODEFORCES
    HANDLE hConsole = GetStdHandle(STD_OUTPUT_HANDLE);
    SetConsoleTextAttribute(hConsole, 10);
    cerr << NAME << " = " << VARIABLE;
    SetConsoleTextAttribute(hConsole, 7);
    cerr << '\n';
#endif
}
#else
#define print(x) 0
#endif
struct pair_hash
{
    template<typename T1, typename T2>
    size_t operator () (const pair<T1, T2> &p) const
    {
        auto h1 = hash<T1> {}(p.first);
        auto h2 = hash<T2> {}(p.second);
        return h1 ^ h2;
    }
};
typedef long long ll;
typedef unsigned long long ull;
const ll INFLL = 2 * (ll)1e18 + 100;
const int INFINT = 2 * (int)1e9 + 100;
//ifstream fin(".in");
//ofstream fout(".out");
void die()
{
    cout << "-1\n";
    exit(0);
}
const int NMAX = 1e6 + 5;
const int MOD = 1e9 + 7; /// careful here (7 or 9, 66.. etc)
const double PI = atan(1) * 4;
const double EPS = 1e-12;

vector<pair<char, int> > m4, m2, other;
int n, m;
map<char, int> cnt;
char sol[200][200];

bool cmp(pair<char, int> l, pair<char, int> r)
{
    return l.second < r.second;
}

int main()
{
    FASTIO;
    cin >> n >> m;
    for1(i, n) for1(j, m)
    {
        char a;
        cin >> a;
        cnt[a]++;
    }
    for(char i = 'a'; i <= 'z'; i++)
    {
        if(!cnt[i]) continue;
        if(cnt[i] % 4 == 0) m4.pb(mp(i, cnt[i]));
        else if(cnt[i] % 2 == 0) m2.pb(mp(i, cnt[i]));
        else other.pb(mp(i, cnt[i]));
    }
    if(other.size() >= 2) return cout << "No", 0;
    if(other.size() && (n % 2 == 0 || m % 2 == 0)) return cout << "No", 0;
    if(!other.empty())
    {
        sol[n / 2 + 1][m / 2 + 1] = other[0].first;
        other[0].second--;
        if(other[0].second)
        {
            if(other[0].second % 4 == 0) m4.pb(other[0]);
            else m2.pb(other[0]);
        }
    }
    sort(all(m2), cmp);
    for1(i, n / 2) for1(j, m / 2)
    {
        if(sol[i][j] != '') continue;
        char cur;
        if(m4.empty() && m2.empty()) return cout << "No", 0;
        if(!m4.empty())
        {
            m4[m4.size() - 1].second -= 4;
            cur = m4.back().first;
            if(m4.back().second == 0) m4.pop_back();
        }
        else
        {
            if(m2.back().second < 4)  return cout << "No", 0;
            m2[m2.size() - 1].second -= 4;
            cur = m2.back().first;
            if(m2.back().second == 0) m2.pop_back();
            sort(all(m2), cmp);
        }

        sol[i][j] = sol[i][m - j + 1] = sol[n - i + 1][j] = sol[n - i + 1][m - j + 1] = cur;
    }
    while(!m4.empty())
    {
        m2.pb(m4.back());
        m4.pop_back();
    }
  /*  for1(i, n)
    {
        for1(j, m) cerr << sol[i][j];
        cerr << '\n';
    }*/

    if(n % 2 == 1)
    {
        int i = n / 2 + 1;
        for1(j, m / 2)
        {
            if(sol[i][j] != '') continue;
            if(m2.empty()) return cout << "No", 0;
            m2[m2.size() - 1].second -= 2;
            char cur = m2.back().first;
            if(m2.back().second == 0) m2.pop_back();
            sol[i][j] = sol[i][m - j + 1] = cur;
        }
    }

    if(m % 2 == 1)
    {
        int j = m / 2 + 1;
        for1(i, n / 2)
        {
            if(sol[i][j] != '') continue;
            if(m2.empty()) return cout << "No", 0;
            m2[m2.size() - 1].second -= 2;
            char cur = m2.back().first;
            if(m2.back().second == 0) m2.pop_back();
            sol[i][j] = sol[n - i + 1][j] = cur;
        }
    }
    cout << "Yes\n";

    return 0;
}


Compiler output:
a.cc:95:25: error: empty character constant
   95 |         if(sol[i][j] != '') continue;
      |                         ^~
a.cc:131:29: error: empty character constant
  131 |             if(sol[i][j] != '') continue;
      |                             ^~
a.cc:145:29: error: empty character constant
  145 |             if(sol[i][j] != '') continue;
      |                             ^~