Hackerrank week code 27 - hackonacci matrix rotation - study Java code

weekcode27_Hackonacci_Matrixrotation.java

public class Solution {
    private static final boolean[] hval = {true, true, false, true, false, false, true};
    private static boolean[][] matrix;
    private static int count90;
    private static int count180;
    private static int count270;

    private static boolean h(long n) {
        int index = (int) (n % 7);
        return hval[index];
    }
    
    private static void buildMatrix(int n) {
        matrix = new boolean[n][n];
        for (int i=1;  i <= n;  i++) {
            for (int j=1;  j <= n;  j++) {
                long val = (long)i * j;
                val *= val;
                matrix[i-1][j-1] = h(val);
            }
        }
    }
    
    private static void countDiffs() {
        final int maxIndex = matrix.length - 1;
        count90 = 0;
        count180 = 0;
        count270 = 0;
        for (int i=0;  i <= maxIndex;  i++) {
            for (int j=0;  j <= maxIndex;  j++) {
                if (matrix[i][j] != matrix[j][maxIndex-i]) count90++;
                if (matrix[i][j] != matrix[maxIndex-i][maxIndex-j]) count180++;
                if (matrix[i][j] != matrix[maxIndex-j][i]) count270++;
            }
        }
    }
    
    private static int countDiffAfterRot(int angle) {
        angle %= 360;
        switch (angle) {
            case 90: return count90;
            case 180: return count180;
            case 270: return count270;
        }
        return 0;
    }
    
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        buildMatrix(n);
        countDiffs();
        int q = in.nextInt();
        for(int a0 = 0; a0 < q; a0++){
            int angle = in.nextInt() % 360;
            // your code goes here
            System.out.println(countDiffAfterRot(angle));
        }
    }
}