sudoku-hint-elimination

import java.util.ArrayList;
import java.util.Arrays;

/**
 * Sudoku
 */
public class Sudoku {
    static void displayBoard(String boardString){
        String[] boardRows = {"", "", "", "", "", "", "", "", ""};
        char[] boardArray = boardString.toCharArray();
        for(int index = 0; index < boardString.length(); index ++ ){
            boardRows[index/9] = boardRows[index/9] + " " + boardArray[index];
            if(index % 9 == 2 || index % 9 == 5){
                boardRows[index/9] = boardRows[index/9] + " |";
            }
        }
        System.out.println("-------------------------");
        for(int index = 0; index < 9; index ++ ){
            System.out.println("|" + boardRows[index] + " |");
            if(index == 2 || index == 5){
                System.out.println("-------------------------");
            }
        }
        System.out.println("-------------------------");
    } 

    static ArrayList<Character> findPossibleSolutions(String boardString, int index){
        ArrayList<Character> possibleSolutions = new ArrayList<Character>(Arrays.asList('1', '2', '3', '4','5','6','7','8','9'));
    
        char[] boardChars = boardString.toCharArray();

        String[] usedNumbersInRow = {"", "", "", "", "", "", "", "", ""};
        for(int i = 0; i < boardString.length(); i ++ ){
            if(boardChars[i] != '_'){
                usedNumbersInRow[i/9] = usedNumbersInRow[i/9] + boardChars[i];
            }
        }

        char[] tempArray = usedNumbersInRow[index/9].toCharArray();

        ArrayList<Character> rowEliminationValues = new ArrayList<Character>() ;
        for(char c: tempArray){
            rowEliminationValues.add(c);
        }

        possibleSolutions.removeAll(rowEliminationValues);

        return possibleSolutions;
    }

    static String solve(String boardString){
        displayBoard(boardString);
        char[] boardChars = boardString.toCharArray();

        for(int index = 0; index < boardChars.length; index ++ ){
            if(boardChars[index] == '_'){
                findPossibleSolutions(boardString, index);
            }
        }

        return "";
    }

    static String guess(String boardString){
        // Variables to keep track

        // Pseudo Code
        // For each cell
        //      If cell is empty
        //          find possible solutions for cell
        //              if there are possible solutions
        //                  take the first solution in list and put into cell
        //              if there are no possible solutions
        //                  backtrack
        //                      find the previous emptyCell which I filled in
        //                      revert to empty
        //                          keep track of the wrong solution
        //                          find possible solutions, exclude the wrong solution, and take the first solution, put into cell


        // Iterations 
        // -----------
        // Iteration 1: Cell at index 1:
            // Guessed Value : 4 
            // Possible solutions: {4,6,7,9}
            // Wrong solutions: {3}
        // Iteration 2: Cell at index 4: 
            // Guessed Value : 
            // Possible solutions: {3,6,7,8}
            // Wrong solutions: {}
        // Iteration 3: Cell at index 6: {}


        return "";
    }


    public static void main(String[] args) {
        // Easy Mode
        String solution = solve("1_58_2____9__764_52__4__819_19__73_6762_83_9_____61_5___76___3_43__2_5_16__3_89__");
        System.out.println("Solution: " + solution);
        System.out.println("Result: "
            + solution.equals("145892673893176425276435819519247386762583194384961752957614238438729561621358947"));
    
        // // Hard Mode
        // String solution =
        // solve("400000805030000000000700000020000060000080400000010000000603070500200000104000000");
        // System.out.println(solution.equals("417369825632158947958724316825437169791586432346912758289643571573291684164875293"));
    }
}