How to create a vector that displays the frequency of each element in a matrix?

Question

"Write a method frequency which receives data from a matrix A that has integers between 0 and x; generates a vector with the occurrences of each integer between 0 and x. Write a method greater that takes an integer vector and returns the largest element of the vector. Write the main module, which fills a matrix only with values between 0 and x and displays which value was the most frequent (call the methods obligatory frequency, greater and leMatriz). "

I’ve already set up the matrix by drawing the numbers, now I’m trying to create the method frequency. I have two doubts:

1) How do I get the algorithm to "jump" the count of numbers that have already been counted? For example, if the matrix is: (0 0 1); (2 3 0); (1 2 3), the program will count 0 three times, then when it passes to the next, it will count 0 three times again.

2) How to declare the vector that will store the counted frequencies without knowing their size? I thought about creating a string and then converting it to an integer vector, but repeating the frequency count would still be a problem. I also thought of leaving the elements of the matrix in ascending order to find the highest value. With this I would know the size of the vector that stores the frequencies. But I’m not able to sort using Arrays.Sort()...

public class Freq_Maior {
    static Scanner ent = new Scanner(System.in);
    public static void main(String[] args) {
        System.out.print("Digite o número de linhas e colunas da matriz: ");
        int m = ent.nextInt();
        int n = ent.nextInt();
        System.out.print("Digite o valor máximo do intervalo usado para preencher a matriz: ");
        int x = ent.nextInt();
        int [][] A = new int[m][n];
        leMatrizR(A, x);

    }
    // método para ler a matriz
    public static void leMatrizR(int matriz[][], int a) {
        Random rnd = new Random();
        for (int i=0; i<matriz.length; i++) {
            for (int j=0; j<matriz[0].length; j++) {               
                matriz[i][j] = rnd.nextInt(a+1);
            }
        }
    } 
    public static void Freq(int matriz[][]) {
        ????
    }
}

Answer 1

Your vector with the frequencies you actually know the size: x + 1, being x the maximum value of the range used to fill the matrix. Then the vector freqs may be declared as:

int [] freqs = new int[x + 1];

Done this, you can pass it to the method Freq and perform the computation of frequencies, and to "skip" the elements already counted, just compare them with the element that we are wanting to count at the moment:

public static void contaFrequencia(int matriz[][], int freqs[]) {
    // para cada elemento possível (0..x)...
    for ( int e = 0; e < freqs.length; e++ ) {
        freqs[e] = 0; // initializa o valor da frequência com 0.
        for ( int i = 0; i < matriz.length; i++ ) {
            for ( int j = 0; j < matriz[i].length; j++ ) {
                // se encontramos o elemento...
                if ( matriz[i][j] == e ) {
                    // incrementamos a frequência do elemento.
                    freqs[e]++;
                }
            }
        }
    }
}