Minimum changes needed to make a 3*3 matrix magic square

Given a 3*3 matrix, find the minimum number of changes that need to be made to it in order to turn it into a magic square. A magic square is a square matrix whose sum of all the rows are the same, the sum of all the columns are the same and the sum of both the diagonals are the same.

Examples:

Input :  8 5 6 
         3 8 7 
         4 9 2 
Output : 2
5 in row 1 col 2 should be changed to 1
8 in row 2 col 2 should be changed to 5
Total 2 changes are required.

Input : 8 9 4 
        5 9 3 
        6 1 8 
Output : 3
8 in row 1 col 1 should be changed to 2
5 in row 2 col 1 should be changed to 7
9 in row 2 col 2 should be changed to 5
Total 3 changes are required.


There are 8 possible magic squares of 3*3 dimensions, which are

8 1 6
3 5 7
4 9 2

6 1 8
7 5 3
2 9 4

4 9 2
3 5 7
8 1 6

2 9 4
7 5 3
6 1 8

8 3 4
1 5 9
6 7 2

4 3 8
9 5 1
2 7 6

6 7 2
1 5 9
8 3 4

2 7 6
9 5 1
4 3 8

We create a 3D array to store these 8 matrices. Now we check the input matrix for each of these 8 matrices and find out the one which can be obtained with the least number of changes.

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class GfG {
  
    // this program takes in two 2D arrays as
    // input and compares them to find out the
    // minimum number of changes that needs to
    // be made to convert arr to ms.
    public static int findMinimumFromMS(int[][] arr,
                                        int[][] ms)
    {
        int count = 0;
        for (int i = 0; i < 3; i++) {
            for (int j = 0; j < 3; j++) {
                if (arr[i][j] != ms[i][j])
                    count++;
            }
        }
        return count;
    }
  
    public static int findMinimum(int[][] arr)
    {
        int[][][] ms = {
            { { 8, 1, 6 }, { 3, 5, 7 }, { 4, 9, 2 } },
            { { 6, 1, 8 }, { 7, 5, 3 }, { 2, 9, 4 } },
            { { 4, 9, 2 }, { 3, 5, 7 }, { 8, 1, 6 } },
            { { 2, 9, 4 }, { 7, 5, 3 }, { 6, 1, 8 } },
            { { 8, 3, 4 }, { 1, 5, 9 }, { 6, 7, 2 } },
            { { 4, 3, 8 }, { 9, 5, 1 }, { 2, 7, 6 } },
            { { 6, 7, 2 }, { 1, 5, 9 }, { 8, 3, 4 } },
            { { 2, 7, 6 }, { 9, 5, 1 }, { 4, 3, 8 } },
        };
  
        // If all the elements need to be changed,
        // there would be 9 changes, so we take the
        // max as 9
        int min = 9;
        for (int i = 0; i < 8; i++) {
            int x = findMinimumFromMS(arr, ms[i]);
            if (x < min)
                min = x;
        }
        return min;
    }
  
    public static void main(String[] args)
    {
        int[][] arr = { { 8, 5, 6 }, { 3, 8, 7 }, 
                                     { 4, 9, 2 } };
        System.out.println(findMinimum(arr));
    }
}

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Output:

2


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