HackerEarth Palindromic grid problem solution

import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.io.BufferedInputStream;
import java.util.PriorityQueue;
import java.util.AbstractCollection;
import java.io.FilterInputStream;
import java.util.Collections;
import java.io.InputStream;

public class Main {
    public static void main(String[] args) {
        new Thread(null, new Runnable() {
            public void run() {
                new Main().solve();
            }
        }, "1", 1 << 26).start();
    }
 
    void solve() {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        ScanReader in = new ScanReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        Plindromicgrid solver = new Plindromicgrid();
        int testCount = in.scanInt();
        for (int i = 1; i <= testCount; i++)
            solver.solve(i, in, out);
        out.close();
    }
 
    static class Plindromicgrid {
        int[] freq;
 
        private int findIndex(int required) {
            int max = -1;
            int index = -1;
            for (int i = 0; i < 26; i++) {
                if (freq[i] >= max) {
                    max = freq[i];
                    index = i;
                }
            }
            if (max < required) return -1;
            return index;
        }
 
        public void solve(int testNumber, ScanReader in, PrintWriter out) {
            int n = in.scanInt();
            int m = in.scanInt();
            freq = new int[26];
            for (int i = 0; i < n; i++)
                for (int j = 0; j < m; j++)
                    freq[(int) in.scanChar() - 97]++;
 
            boolean ans = true;
            boolean[][] visited = new boolean[n][m];
            PriorityQueue<Integer> priorityQueue = new PriorityQueue<>(Collections.reverseOrder());
 
            out:
            for (int i = 0; i < n; i++) {
                for (int j = 0; j < m; j++) {
                    if (visited[i][j]) continue;
                    int required = 4;
                    if (i == n - i - 1) required -= 2;
                    if (j == m - j - 1) required -= 2;
                    required = Math.max(required, 1);
                    priorityQueue.add(required);
                    visited[i][j] = true;
                    visited[n - i - 1][j] = true;
                    visited[i][m - j - 1] = true;
                    visited[n - i - 1][m - j - 1] = true;
                }
            }
            while (!priorityQueue.isEmpty()) {
                int required = priorityQueue.poll();
                int index = findIndex(required);
                if (index == -1) ans = false;
                else freq[index] -= required;
            }
            if (ans) out.println("YES");
            else out.println("NO");
        }
 
    }
 
    static class ScanReader {
        private byte[] buf = new byte[4 * 1024];
        private int index;
        private BufferedInputStream in;
        private int total;
 
        public ScanReader(InputStream inputStream) {
            in = new BufferedInputStream(inputStream);
        }
 
        private int scan() {
            if (index >= total) {
                index = 0;
                try {
                    total = in.read(buf);
                } catch (Exception e) {
                    e.printStackTrace();
                }
                if (total <= 0) return -1;
            }
            return buf[index++];
        }
 
        public char scanChar() {
            int c = scan();
            while (isWhiteSpace(c)) c = scan();
            return (char) c;
        }
 
        public int scanInt() {
            int integer = 0;
            int n = scan();
            while (isWhiteSpace(n)) n = scan();
            int neg = 1;
            if (n == '-') {
                neg = -1;
                n = scan();
            }
            while (!isWhiteSpace(n)) {
                if (n >= '0' && n <= '9') {
                    integer *= 10;
                    integer += n - '0';
                    n = scan();
                }
            }
            return neg * integer;
        }
 
        public String next() {
            int c = scan();
            if (c == -1) return null;
            while (isWhiteSpace(c)) c = scan();
            StringBuilder res = new StringBuilder();
            do {
                res.appendCodePoint(c);
                c = scan();
            } while (c != 'n' && c != -1);
            return res.toString();
        }
 
        private boolean isWhiteSpace(int n) {
            if (n == ' ' || n == 'n' || n == 'r' || n == 't' || n == -1) return true;
            else return false;
        }
 
    }
}