Check if all 9 digits are in 3*3 2d array in java

Question

I'm working on problem where I have to check if all 9 digits are in 3x3 matrix.
I know that I should loop over the 3x3 matrix and check for each number is digit or not. Here is my code, but I don't have directions to do it.

public boolean find(int num) {
    int []a = {1, 2, 3, 4, 5, 6, 7, 8, 9};

    for (int i = 0; i < a.length; i++)
        if (a[i] == num)
            return true;
    return false;
}

public boolean allDigit() {  
    boolean isDigit = true;
    for (int i = 0; i< _3x3.length; i++) {
        for(int j = 0; j < _3x3[i].length; j++) {
            if (!find(_3x3[i][j]))
                isDigit = false;
        }
    }
}

Answer 1

The presented code contains several typos:

• type of num parameter in find has to be int
• method allDigit should return isDigit in the end
• input matrix _3x3 needs to be defined and populated somewhere, or passed to allDigit as an argument.

After fixing the mentioned issues the code should detect if all the numbers in _3x3 array belong to the closed range [1, 9] , that is, if the input matrix contains 1 in all its cells, the code returns true .

However, if the purpose of the task is to check that the input matrix contains all digits , that is, there is no duplicate entry, then the separate find method should not be called. Instead a boolean array is needed to check for duplicate entries:

public boolean allDigitsPresent(int[][] arr) {
    boolean[] digitSet = new boolean[10];
    for (int i = 0; i < arr.length; i++) {
        for (int j = 0; j < arr[i].length; j++) {
            int d = arr[i][j]; // digit
            if (d <= 0 || d >= digitSet.length) {
                return false; // invalid value in the matrix
            }
            if (digitSet[d]) { // already set, duplicate is found
                return false;
            }
            digitSet[d] = true;
        }
    }
    return true; // no duplicate digit is found, all digits are in range [1..9]
}