Code is not giving expected result in sudoku

Question

I have written the basic logic to match 2D array, but the result are bit unexpected

if(mat1[i][j] == mat2[i][j]) //what this line do

public static final int[][] n_1 = {{10,12,6,-1,-1},{-1,0,8,2,-1},{0,0,0,-1,0},{0,0,0,0,0},{-1,9,0,0,-1}};
public static final int[][] n_2 = {{13,-1,9,6,0},{0,-1,-1,0,0},{0,0,0,0,0},{-1,4,7,-1,0},{-1,2,8,0,0}};
public static final int[][] n_3 = {{-1,0,0,-1,-1},{0,0,0,11,-1},{0,0,0,5,-1},{8,0,0,0,13},{10,-1,6,4,0}};
public static final int[][] n_4 = {{10,8,0,1,-1},{13,0,0,3,-1},{0,0,0,-1,-1},{0,0,5,0,-1},{7,0,0,0,-1}};
public static final int[][] n_5 = {{-1,0,0,6,0},{-1,0,0,0,0},{12,0,5,-1,0},{0,0,3,-1,0},{4,-1,-1,-1,1}};

public static int[][][] arrayFive = {n_1,n_2,n_3,n_4,n_5};  
public static int [][] return5(){
    Random r = new Random();
    return arrayFive[r.nextInt(arrayFive.length)];
}

public boolean checkEqual(int[][] mat1,int[][] mat2){
    boolean b = true;
    for(int i = 0;i<mat1.length;i++){
        for(int j=0;j<mat1.length;j++){
            if(mat1[i][j] == mat2[i][j]){
                b = b & true;
            }
            else{
                b = b &false;
            }
        }
    }
    return b;
}

`if(mat1[i][j] == mat2[i][j])` is just doing an int comparision. if mat1 is n_1 and mat2 is n_2 the loop is just check whether 10 == 13, 12 == -1 and so on. — Syam S, Jul 25 '14 at 10:20
@Mann That is just just checkking the elements inside mat and mat2. By the way there is a typo as well. — Suresh Atta, Jul 25 '14 at 10:20
It should rather be `if (mat1[i][j] != mat2[i][j]) return false`. No need to check the other elements in that case. — isnot2bad, Jul 25 '14 at 10:35

score 2 · Accepted Answer · answered Jul 25 '14 at 10:49

This line:

        if (mat1[i][j] == mat2[i][j])

is testing to see if the corresponding elements of the 2 matrices have the same value.

Looking at it in context:

        if(mat1[i][j] == mat2[i][j]){
            b = b & true;
        }
        else{
            b = b &false;
        }

is a rather cumbersome way of saying this:

        if(mat1[i][j] != mat2[i][j]){
            b = false;
        }

But you could rewrite the checkEqual method to this:

public boolean checkEqual(int[][] mat1,int[][] mat2){
    for(int i = 0;i<mat1.length;i++){
        for(int j=0;j<mat1.length;j++){
            if(mat1[i][j] != mat2[i][j]){
                return false;
            }
        }
    }
    return true;
}

which is a whole lot faster in the case where the matrices are not equal.

Finally, it is worth noting that the code assumes that the two matrices are square, and they have the same size. If either of those assumptions is false, the method will throw an exception.

@Mann - yes, in this example, they obviously are. But if this code was used in a larger application, that assumption may not always be correct. — Stephen C, Jul 25 '14 at 11:19

Code is not giving expected result in sudoku

1 Answers1