content: package LeetCode.Medium.ValidSudoku;
  
  /*
    36. Valid Sudoku
  
    Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:
  
    Each row must contain the digits 1-9 without repetition.
    Each column must contain the digits 1-9 without repetition.
    Each of the nine 3 x 3 sub-boxes of the grid must contain the digits 1-9 without repetition.
    Note:
    A Sudoku board (partially filled) could be valid but is not necessarily solvable.
    Only the filled cells need to be validated according to the mentioned rules.
  
  
    Example 1:
    Input: board =
    [["5","3",".",".","7",".",".",".","."]
    ,["6",".",".","1","9","5",".",".","."]
    ,[".","9","8",".",".",".",".","6","."]
    ,["8",".",".",".","6",".",".",".","3"]
    ,["4",".",".","8",".","3",".",".","1"]
    ,["7",".",".",".","2",".",".",".","6"]
    ,[".","6",".",".",".",".","2","8","."]
    ,[".",".",".","4","1","9",".",".","5"]
    ,[".",".",".",".","8",".",".","7","9"]]
    Output: true
  
  
    Example 2:
    Input: board =
    [["8","3",".",".","7",".",".",".","."]
    ,["6",".",".","1","9","5",".",".","."]
    ,[".","9","8",".",".",".",".","6","."]
    ,["8",".",".",".","6",".",".",".","3"]
    ,["4",".",".","8",".","3",".",".","1"]
    ,["7",".",".",".","2",".",".",".","6"]
    ,[".","6",".",".",".",".","2","8","."]
    ,[".",".",".","4","1","9",".",".","5"]
    ,[".",".",".",".","8",".",".","7","9"]]
    Output: false
  
    Explanation: Same as Example 1, except with the 5 in the top left corner being modified to 8. Since there are two 8's in the top left 3x3 sub-box, it is invalid.
  
  
    Constraints:
    board.length == 9
    board[i].length == 9
    board[i][j] is a digit or '.'.
  */
  
  /**
   * Solution
   */
  public class Solution {
    private boolean isValidSudoku(char[][] board, int row, int col, char target) {
      // Check the current row
      for (int i = 0; i < 9; i++) {
        if (i == row) continue;
  
        if (board[i][col] == target) return false;
      }
  
      // Check the current column
      for (int j = 0; j < 9; j++) {
        if (j == col) continue;
  
        if (board[row][j] == target) return false;
      }
  
      int startRow = row - (row % 3);
      int startCol = col - (col % 3);
  
      // Check the current box
      for (int i = 0; i < 3; i++)
        for (int j = 0; j < 3; j++) {
          if (i + startRow == row && j + startCol == col) continue;
  
          if (board[i + startRow][j + startCol] == target) return false;
        }
  
      return true;
    }
  
    public boolean isValidSudoku(char[][] board) {
      for (int row = 0; row < 9; row++)
        for (int col = 0; col < 9; col++) {
          if (board[row][col] == '.') continue;
  
          if (!isValidSudoku(board, row, col, board[row][col])) return false;
        }
  
      return true;
    }
  
    public static void main(String[] args) {
      Solution solution = new Solution();
  
      // should be true
      System.out.println(
          solution.isValidSudoku(
              new char[][] {
                {'5', '3', '.', '.', '7', '.', '.', '.', '.'},
                {'6', '.', '.', '1', '9', '5', '.', '.', '.'},
                {'.', '9', '8', '.', '.', '.', '.', '6', '.'},
                {'8', '.', '.', '.', '6', '.', '.', '.', '3'},
                {'4', '.', '.', '8', '.', '3', '.', '.', '1'},
                {'7', '.', '.', '.', '2', '.', '.', '.', '6'},
                {'.', '6', '.', '.', '.', '.', '2', '8', '.'},
                {'.', '.', '.', '4', '1', '9', '.', '.', '5'},
                {'.', '.', '.', '.', '8', '.', '.', '7', '9'}
              }));
  
      // should be false
      System.out.println(
          solution.isValidSudoku(
              new char[][] {
                {'8', '3', '.', '.', '7', '.', '.', '.', '.'},
                {'6', '.', '.', '1', '9', '5', '.', '.', '.'},
                {'.', '9', '8', '.', '.', '.', '.', '6', '.'},
                {'8', '.', '.', '.', '6', '.', '.', '.', '3'},
                {'4', '.', '.', '8', '.', '3', '.', '.', '1'},
                {'7', '.', '.', '.', '2', '.', '.', '.', '6'},
                {'.', '6', '.', '.', '.', '.', '2', '8', '.'},
                {'.', '.', '.', '4', '1', '9', '.', '.', '5'},
                {'.', '.', '.', '.', '8', '.', '.', '7', '9'}
              }));
    }
  }
  