HackerEarth Palindromic grid problem solution

In this HackerEarth Palindromic grid problem solution, You are given a 2-d grid of N rows and M columns containing lower case alphabets only. You need to check whether it is possible to rearrange the complete grid so that each row and column becomes palindromic.

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;
        }
 
    }
}