Sudoku.java

import java.util.HashSet;
import java.util.Set;

public class Sudoku {

  public static boolean checkRow(int[][] sudoku) {
    for (int i = 0; i < 9; i++) {
      Set<Integer> row = new HashSet<Integer>();
      for(int j = 0; j < 9; j++) {
        if (sudoku[i][j] != 0) {
          row.add(new Integer(sudoku[i][j]));
        }
      }
      if (row.size() != 9) {
        return false;
      }
    }
    return true;
}

  public static boolean checkColumn(int [][] sudoku) {
    for (int i = 0; i < 9; i++) {
      Set<Integer> column = new HashSet<Integer>();
      for(int j = 0; j < 9; j++) {
        if (sudoku[j][i] != 0) {
          column.add(new Integer(sudoku[j][i]));
        }
      }
      if (column.size() != 9) {
        return false;
      }
    }
    return true;
  }

  public static boolean checkOneBox(int [][] sudoku, int a, int b) {
    Set<Integer> box = new HashSet<Integer>();
    for (int i = a*3; i < a*3 + 3; i++) {
      for(int j = b*3; j < b*3 + 3; j++) {
        if (sudoku[i][j] != 0) {
          box.add(new Integer(sudoku[i][j]));
        }
      }
    }
    if (box.size() != 9) {
        return false; 
    }
    return true;
  }

  public static boolean checkAllBoxes(int [][]sudoku) {
    for (int a = 0; a < 3; a++) {
      for (int b = 0; b < 3; b++){
        boolean checkAllBox = checkOneBox(sudoku, a, b);
        if (!checkAllBox) {
          return false;
        }
      }
    }
    return true;
}
  

  public static void main(String[] args) {
    int[][] sudoku = new int[][] {
      { 2, 1, 3, 4, 5, 0, 7, 9, 8 },
      { 9, 0, 6, 0, 2, 7, 3, 0, 4 },
      { 5, 4, 0, 3, 0, 9, 1, 2, 6 },
      { 1, 0, 2, 0, 6, 4, 5, 7, 0 },
      { 6, 7, 0, 5, 0, 3, 0, 4, 1 },
      { 0, 3, 0, 0, 1, 0, 8, 0, 9 },
      { 0, 6, 1, 0, 0, 5, 0, 8, 2 },
      { 0, 0, 4, 6, 3, 0, 9, 0, 5 },
      { 8, 0, 0, 0, 4, 1, 6, 3, 7 }
    };

    int[][] correctSudoku = new int[][] {
      { 5, 3, 4, 6, 7, 8, 9, 1, 2 },
      { 6, 7, 2, 1, 9, 5, 3, 4, 8 },
      { 1, 9, 8, 3, 4, 2, 5, 6, 7 },
      { 8, 5, 9, 7, 6, 1, 4, 2, 3 },
      { 4, 2, 6, 8, 5, 3, 7, 9, 1 },
      { 7, 1, 3, 9, 2, 4, 8, 5, 6 },
      { 9, 6, 1, 5, 3, 7, 2, 8, 4 },
      { 2, 8, 7, 4, 1, 9, 6, 3, 5 },
      { 3, 4, 5, 2, 8, 6, 1, 7, 9 }
    };

    for(int i=0; i<9; i++){
      for (int j=0; j<9; j++) {
        if(sudoku[i][j]==0)
          System.out.print(" ");
        else
          System.out.print(sudoku[i][j]);
        if (j % 3 == 2 && j!=8)
          System.out.print("|");
        if(j==8)
          System.out.println();
      }

      if(i%3 == 2 && i!=8)
        System.out.println("---+---+---");

    }

  boolean checkRow = checkRow(correctSudoku);
  System.out.println("Row result:" + checkRow);
  boolean checkColumn = checkColumn(correctSudoku);
  System.out.println("Column result:" + checkColumn);
  boolean checkAllBoxes = checkAllBoxes(correctSudoku);
  System.out.println("All Boxes:" + checkAllBoxes);

  }
}import java.util.HashSet;
import java.util.Set;

public class Sudoku {

  public static boolean checkRow(int[][] sudoku) {
    for (int i = 0; i < 9; i++) {
      Set<Integer> row = new HashSet<Integer>();
      for(int j = 0; j < 9; j++) {
        if (sudoku[i][j] != 0) {
          row.add(new Integer(sudoku[i][j]));
        }
      }
      if (row.size() != 9) {
        return false;
      }
    }
    return true;
}

  public static boolean checkColumn(int [][] sudoku) {
    for (int i = 0; i < 9; i++) {
      Set<Integer> column = new HashSet<Integer>();
      for(int j = 0; j < 9; j++) {
        if (sudoku[j][i] != 0) {
          column.add(new Integer(sudoku[j][i]));
        }
      }
      if (column.size() != 9) {
        return false;
      }
    }
    return true;
  }

  public static boolean checkOneBox(int [][] sudoku, int a, int b) {
    Set<Integer> box = new HashSet<Integer>();
    for (int i = a*3; i < a*3 + 3; i++) {
      for(int j = b*3; j < b*3 + 3; j++) {
        if (sudoku[i][j] != 0) {
          box.add(new Integer(sudoku[i][j]));
        }
      }
    }
    if (box.size() != 9) {
        return false; 
    }
    return true;
  }

  public static boolean checkAllBoxes(int [][]sudoku) {
    for (int a = 0; a < 3; a++) {
      for (int b = 0; b < 3; b++){
        boolean checkAllBox = checkOneBox(sudoku, a, b);
        if (!checkAllBox) {
          return false;
        }
      }
    }
    return true;
}
  

  public static void main(String[] args) {
    int[][] sudoku = new int[][] {
      { 2, 1, 3, 4, 5, 0, 7, 9, 8 },
      { 9, 0, 6, 0, 2, 7, 3, 0, 4 },
      { 5, 4, 0, 3, 0, 9, 1, 2, 6 },
      { 1, 0, 2, 0, 6, 4, 5, 7, 0 },
      { 6, 7, 0, 5, 0, 3, 0, 4, 1 },
      { 0, 3, 0, 0, 1, 0, 8, 0, 9 },
      { 0, 6, 1, 0, 0, 5, 0, 8, 2 },
      { 0, 0, 4, 6, 3, 0, 9, 0, 5 },
      { 8, 0, 0, 0, 4, 1, 6, 3, 7 }
    };

    int[][] correctSudoku = new int[][] {
      { 5, 3, 4, 6, 7, 8, 9, 1, 2 },
      { 6, 7, 2, 1, 9, 5, 3, 4, 8 },
      { 1, 9, 8, 3, 4, 2, 5, 6, 7 },
      { 8, 5, 9, 7, 6, 1, 4, 2, 3 },
      { 4, 2, 6, 8, 5, 3, 7, 9, 1 },
      { 7, 1, 3, 9, 2, 4, 8, 5, 6 },
      { 9, 6, 1, 5, 3, 7, 2, 8, 4 },
      { 2, 8, 7, 4, 1, 9, 6, 3, 5 },
      { 3, 4, 5, 2, 8, 6, 1, 7, 9 }
    };

    for(int i=0; i<9; i++){
      for (int j=0; j<9; j++) {
        if(sudoku[i][j]==0)
          System.out.print(" ");
        else
          System.out.print(sudoku[i][j]);
        if (j % 3 == 2 && j!=8)
          System.out.print("|");
        if(j==8)
          System.out.println();
      }

      if(i%3 == 2 && i!=8)
        System.out.println("---+---+---");

    }

  boolean checkRow = checkRow(correctSudoku);
  System.out.println("Row result:" + checkRow);
  boolean checkColumn = checkColumn(correctSudoku);
  System.out.println("Column result:" + checkColumn);
  boolean checkAllBoxes = checkAllBoxes(correctSudoku);
  System.out.println("All Boxes:" + checkAllBoxes);

  }
}