package Project_3;

import java.util.Scanner;
import java.io.FileReader;
import java.io.IOException;


public class Project1 
{

  public static int[][] board = new int[6][6];

  public Project1() {
    
  }

  public boolean trySolving(int row, int column)
  {
    int counter = 0;
    if (this.board[row-1][column-1] == 0) // is this spot open? (-1 because using 1-6 as numbers buy array is 0-5
    {
      
      for (int possibleValues = 1; possibleValues <= 6; possibleValues++) //tries all possible values
      {
        
        if ( (!this.doesRowContainValue(possibleValues, row-1, column-1)) && (!this.doesColumnContainValue(possibleValues, row-1, column-1)) && (!this.doesSquareContainValue(possibleValues, row, column)) ) //makes sure the number is not in the row, column, or box
        {
          this.board[row - 1][column - 1] = possibleValues; //add the value to the square
          
          //if at end of row, and not on the last row, go to beginning of next row
          if ( (column == 6) && (row < 6)) {
            row++;
            column = 0;
          }
          
          if (column < 6)
            return trySolving(row, column + 1); //moves right 1 square if not at the end of the row
          else if (row < 6)
            return trySolving(row + 1, column); //moves down 1 square if not at the end of the coloumn
          else
            return true;                   //reached the end of the puzzle
        }
        
        
        else   // value did not work
          counter++;                    //keeps track of how many numbers fail
        
      }//end of for loop
      
      
      if (counter == 6)                 // none of the 6 values worked in this square
        return false;
    }
    
    
  //-----------------------------------------Already a value on this spot!------------------------------------
    //if at end of row, and not on the last row, go to beginning of next row
    if ( (column == 6) && (row < 6)) 
    {
      row++;
      column = 0;
    }
    if (column < 6) //spot was not open, so moving to the next spot
      return trySolving(row, column + 1); //moves right 1 square if not at the end of the row
    else if (row < 6)
      return trySolving(row + 1, column);        //moves down 1 square if not at the end of the coloumn
    else
      return true;                        //reached the end of the puzzle
  //---------------------------------Already a value on this spot!--------------------------------------------
    
  }
  
  /*
   * doesRowContainValue
   * pre - Existing sudoku board
   * post - determines if current row contains the current value
   * @return - Returns true if current row contains the current value
   */
  private boolean doesRowContainValue(int value, int row, int column)
    {
        for (int columnindex = 0; columnindex <= 5; columnindex++)
        {
            if ((this.board[row][columnindex] == value) && (column != columnindex))
            {
                return true;
            }
        }
        return false;
    }
    
    
    /*
     * doesColumnContainValue
     * pre - Existing sudoku board
     * post - determines if current column contains the current value
     * @return - Returns true if current column contains the current value
     */
    private boolean doesColumnContainValue(int value, int row, int column)
    {
        for (int rowindex = 0; rowindex <= 5; rowindex++)
        {
            if ((this.board[rowindex][column] == value) && (row != rowindex) )
            {
                return true;
            }
        }
        return false;
    }


    /*
     * doesSquareContainValue
     * pre - Existing sudoku board
     * post - determines if current square contains the current value
     * @return - Returns true if current square contains the current value
     */
    private boolean doesSquareContainValue(int value, int row, int column) 
    {
      //identify square
      int rowStart = ( (row - 1) / 2) + 1;
      int columnStart = ( (column - 1) / 3) + 1;
      int rowIndexEnd = rowStart * 2;
      if (rowIndexEnd == 0) 
        rowIndexEnd = 3;
      int rowIndexStart = rowIndexEnd - 1;
      int columnIndexEnd = columnStart * 3;
      if (columnIndexEnd == 0) 
        columnIndexEnd = 3;
      int columnIndexStart = columnIndexEnd - 2;
      for (int rowIndex = rowIndexStart; rowIndex <= rowIndexEnd; rowIndex++) 
      {
        for (int columnIndex = columnIndexStart+1; columnIndex <= columnIndexEnd; columnIndex++) 
        {
          if ( (this.board[rowIndex][columnIndex] == value) )
          {
            return true;
          }
        }
      }
      return false;
    }
    
    
    public void main(String[] args)
    {
      try {
        System.out.println("Please enter the name of the sudoku file: ");
        Scanner sudokuName = new Scanner(System.in);
        String name = sudokuName.nextLine();
        FileReader reader = new FileReader(name);
        Scanner in = new Scanner(reader);
        for (int i = 0; i < 6 ; i++) 
        {
          for (int j = 0; j < 6; j++) 
          {
            board[i][j] = in.nextInt();
          }
        }
        if (trySolving(1, 1)) 
        {
          System.out.println("Puzzle was successfully solved");
          for (int i = 0; i < 6; i++) 
          {
            for (int j = 0; j < 6; j++) 
            {
              System.out.print(board[i][j] + " ");
              if (j == 5)
                System.out.println();
            }
          }
        }
      }
      catch (IOException exception)
      {
        System.out.println("Error processing file: " + exception);
      }
    }
  
}