Suri's Sudoku Solver (SSS)

My version of the MATLAB Sudoku solver, which employs recursive function to arrive at a solution

Suri's Sudoku Solver (SSS)

DESCRIPTION:
This function is a sudoku puzzle solver that uses a recursive algorithm described below.

Step 1. Take a standard sudoku puzzle in matrix form with all the blank spots filled with zeros. For example, you could type

puzzle=[7 0 0 5 8 3 0 0 6; 0 0 6 0 0 1 4 0 5; 0 5 2 0 0 6 0 8 3; 3 0 0 2 0 0 9 5 8; 5 0 0 0 7 8 0 6 0; 6 4 8 0 1 0 3 0 0; 0 6 0 8 0 2 5 0 0; 0 0 3 1 5 0 0 7 2; 2 1 5 6 0 0 0 3 0]

and MATLAB will give you

puzzle =
7 0 0 5 8 3 0 0 6
0 0 6 0 0 1 4 0 5
0 5 2 0 0 6 0 8 3
3 0 0 2 0 0 9 5 8
5 0 0 0 7 8 0 6 0
6 4 8 0 1 0 3 0 0
0 6 0 8 0 2 5 0 0
0 0 3 1 5 0 0 7 2
2 1 5 6 0 0 0 3 0

Step 2. Find the locations of all zeros. For each of them, determine which numbers (between 1 and 9) are missing in the row, column and 3x3 box (region) that the zero belongs to. For example, the first zero in the first row in the example above belongs to row 1 ( 7 0 0 5 8 3 0 0 6 ), column 2 ( 0 0 5 0 0 4 6 0 1 ) and the top-left region ( 7 0 0; 0 0 6; 0 5 2 ).

Step 3. The function determines that the numbers ( 1 2 4 9 ) are missing in row 1, the numbers ( 2 3 7 8 9 ) are missing in column 2, and finally the numbers ( 1 3 4 8 9 ) are missing in the top-left region.

Step 4. The intersection ( common elements ) of the three arrays found in Step 3 is calculated. In this case, the only number that are common to the three arrays above is 9. The function then fills the number 9 to the location (1, 2) to replace the zero. However, if the intersection of the three arrays has more than one number, the zero is not replaced with any number and the incomplete puzzle will be fed into this function again. This is where the recursion occurs. The recursion continues until all zeros in the puzzle are replaced with numbers (between 1 and 9). Then the result (solved puzzle) will be displayed.

HOW TO USE THIS FUNCTION:
Simply place the files 'sudoku.m', 'rcb.m' and 'whichbox.m' in the same folder, navigate to that folder in MATLAB, and then type up the puzzle in the matrix form as shown in Step 1. Then just call the function in Command Window by typing 'result = sudoku(puzzle)' and hit enter.