Language: C++

#include <bits/stdc++.h>

using namespace std;

#define all(c) (c).begin(), (c).end()
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};

int H, W;
char a[102][102];

bool ok(const string &s) {
    auto n = s.size();
    auto s1 = s.substr(0, n / 2);
    auto s2 = s.substr(n / 2 + n % 2, n / 2);
    reverse(all(s2));
    return s1 == s2;
}

bool ok(const vector<char> &vec) {
    rep(i, H) {
        string s = "";
        rep(j, W) s += vec[i * W + j];
        if (!ok(s)) return false;
    }
    rep(i, W) {
        string s = "";
        rep(j, H) s += vec[i + j * W];
        if (!ok(s)) return false;
    }

    return true;
}

void naive() {
    vector<char> vec;
    rep(i, H) rep(j, W) vec.push_back(a[i][j]);
    sort(all(vec));

    do {
        if (ok(vec)) {
            rep(i, H) {
                rep(j, W) { cout << vec[i * W + j]; }
                cout << " ";
            }
            cout << endl;
        }
    } while (next_permutation(all(vec)));
}

int main() {
    cin >> H >> W;
    rep(i, H) rep(j, W) cin >> a[i][j];

    int cnt[26] = {};
    rep(i, H) rep(j, W) cnt[a[i][j] - 'a']++;
    // rep(i, 26) if (cnt[i]) cout << char(i + 'a') << ": " << cnt[i] << endl;

    int cnt2[4] = {};
    int mod2[2] = {} rep(i, 26) cnt2[cnt[i] % 4]++;
    rep(i, 26) mod2[cnt[i] % 2]++;
    int sum = 0;
    rep(i, 4) sum += cnt2[i];
    if (H == 1 || W == 1) {
        int odd_cnt = 0;
        rep(i, 26) odd_cnt += cnt[i] % 2;
        if ((H + W) % 2 == 1) {
            if (odd_cnt == 0) {
                cout << "Yes" << endl;
            } else {
                cout << "No" << endl;
            }
        } else {
            if (odd_cnt == 1) {
                cout << "Yes" << endl;
            } else {
                cout << "No" << endl;
            }
        }
        return 0;
    }
    if (H % 2 == 1 && W % 2 == 1) {
        if (cnt2[1] != 1) {
            cout << "No" << endl;
            return 0;
        }
        if (cnt[2] != 0 || cnt[2] != (H + W - 2) / 2) {
            cout << "No" << endl;
        }
        if (cnt2[1] + cnt2[0] + cnt[2] != sum) {
            cout << "No" << endl;
            return 0;
        }
        cout << "Yes" << endl;
        return 0;
    }
    if (H % 2 == 0 && W % 2 == 0) {
        if (cnt2[0] != sum) {
            cout << "No" << endl;
            return 0;
        }
        cout << "Yes" << endl;
        return 0;
    }
    if (H % 2 == 1 || W % 2 == 1) {
        int t = H;
        if (W % 2 == 0) t = W;
        // cout << cnt2[2] << ", " << t / 2 << endl;
        if (cnt2[2] != t / 2) {
            cout << "No" << endl;
            return 0;
        }
        if (cnt2[2] + cnt2[0] != sum) {
            cout << "No" << endl;
            return 0;
        }
        cout << "Yes" << endl;
        return 0;
    }
    assert(false);

    return 0;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:6:19: error: expected ',' or ';' before 'for'
    6 | #define rep(i, n) for (int i = 0; i < (int)(n); i++)
      |                   ^~~
a.cc:62:22: note: in expansion of macro 'rep'
   62 |     int mod2[2] = {} rep(i, 26) cnt2[cnt[i] % 4]++;
      |                      ^~~
a.cc:62:26: error: 'i' was not declared in this scope
   62 |     int mod2[2] = {} rep(i, 26) cnt2[cnt[i] % 4]++;
      |                          ^
a.cc:6:35: note: in definition of macro 'rep'
    6 | #define rep(i, n) for (int i = 0; i < (int)(n); i++)
      |                                   ^