(SPOJ) Quadrado mágico - Solution

Link to the problem: http://br.spoj.com/problems/MAGICO11/

In order to solve this problem, it is only necessary to check if the numbers are valid, if all the numbers between 1 and size^2 are being used exactly once and if the sums (row, column, diagonal) are equal.


import java.io.*;
import java.util.*;

class Main {
    public static int reader(BufferedReader br) throws NumberFormatException, IOException {     
        int n;
        int resp = 0;     
      
        while (true) {         
            n = br.read();         
            if (n >= '0' && n <= '9') {
                break;
            }
        }
           
        while (true) {         
            resp = resp*10 + n-'0';         
            n = br.read();         
            if (n < '0' || n > '9') {
                break;     
            }
        }
      
        return resp;     
    }
   
    public void process() throws NumberFormatException, IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
       
        int size = reader(br);
        int[][] matrix = new int[size][size];
        int[] numbers = new int[size*size + 1];
        for (int i = 0; i < size; i++) {
            for (int j = 0; j < size; j++) {
                matrix[i][j] = reader(br);
                if (matrix[i][j] > size*size) { // if it is not a valid value
                    System.out.println("0");
                    return;
                }
                numbers[matrix[i][j]] = 1;
            }
        }
        br.close();
       
        // check if all the values are present
        for (int i = 1; i <= size*size; i++) {
            if (numbers[i] == 0) {
                System.out.println("0");
                return;
            }
        }
       
        int sumPart = 0;
        HashSet<Integer> sum = new HashSet<>();
        // check sum of lines
        for (int i = 0; i < size; i++) {
            sumPart = 0;
            for (int j = 0; j < size; j++) {
                sumPart += matrix[i][j];
            }
            sum.add(sumPart);
            if (sum.size() > 1) {
                System.out.println("0");
                return;
            }
        }
       
        // check sum of columns
        for (int i = 0; i < size; i++) {
            sumPart = 0;
            for (int j = 0; j < size; j++) {
                sumPart += matrix[j][i];
            }
            sum.add(sumPart);
            if (sum.size() > 1) {
                System.out.println("0");
                return;
            }
        }
       
        // check sum of diagonals
        sumPart = 0;
        for (int i = 0; i < size; i++) {
            sumPart += matrix[i][i];
        }
        int col = size-1;
        sumPart = 0;
        for (int i = 0; i < size; i++) {
            sumPart += matrix[i][col--];
        }
        sum.add(sumPart);
        if (sum.size() > 1) {
            System.out.println("0");
            return;
        }
       
        System.out.println(sumPart);
        
        return;
    }
   
    public static void main(String[] args) throws NumberFormatException, IOException {
        Main m = new Main();
        m.process();
       
        System.exit(0);
    }
}