Overview:
I was ecstatic to receive this project because I play Sudoku often and this was no new problem for me to tackle. This problem strongly reminded me of the 8-Queens problem that I have solved in my 211 - OOP C++ class. The goal of that project was to place as many queens possible in an 8 by 8 grid. The approach that we were taught to pursue was to place a queen on the first tile and try to place the next. If the next cannot be placed, try the next place and so on fourth.
General Structure:
Originally, I tackled this with the same approach (8-Queens); I have placed the first available digit in the first available slot. If that number is valid, it will recursively try to place the next number. If the number is not valid in the next placement of the Sudoku, it will increment the previous cell by backtracking using recursion's natural stack data structure. The new way my program now solves the Sudoku grid is to find a cell with the least number of elements and try to find the coordinates which are available to have a number placed in them.
The CSV files are an interesting twist to add to this project; I spent more time trying to find a good way to read them than implementing an algorithm to solve the Sudoku. After finding a good way to parse the file into the "SudokuGrid" object, I was finally satisfied with storing the 2-dimensional layout to a 1-dimensional array of size 81 (9 by 9 grid).
How to use (Input Output):
There is no direct interface to use with this program. Simply have four CSV files named "easy0.csv" "easy1.csv" "hard0.csv" and "hard1.csv" containing the Sudoku values; respectively, the program will output files starting from 0.csv to 3.csv with the solutions in CSV format.
Exception Handling: If there is a file that cannot be parsed, there will be an exception thrown into System.out and will skip the file that threw an error. If there is an output file IO exception, there will be a null pointer exception following the error result and the program will stop running. This will be treated as a fatal exception as there should be space for a file to be written to.