package com.hit.basmath.learn.hash_table;

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

/**
 * 36. Valid Sudoku
 * <p>
 * Determine if a 9x9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:
 * <p>
 * Each row must contain the digits 1-9 without repetition.
 * Each column must contain the digits 1-9 without repetition.
 * Each of the 9 3x3 sub-boxes of the grid must contain the digits 1-9 without repetition.
 * <p>
 * A partially filled sudoku which is valid.
 * <p>
 * The Sudoku board could be partially filled, where empty cells are filled with the character '.'.
 * <p>
 * Example 1:
 * <p>
 * Input:
 * <p>
 * [
 * ["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"]
 * ]
 * <p>
 * Output: true
 * <p>
 * Example 2:
 * <p>
 * Input:
 * <p>
 * [
 * ["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"]
 * ]
 * <p>
 * Output: false
 * <p>
 * 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.
 * <p>
 * Note:
 * <p>
 * 1. A Sudoku board (partially filled) could be valid but is not necessarily solvable.
 * 2. Only the filled cells need to be validated according to the mentioned rules.
 * 3. The given board contain only digits 1-9 and the character '.'.
 * 4. The given board size is always 9x9.
 */
public class _36 {
    public boolean isValidSudoku(char[][] board) {
        Set<String> seen = new HashSet<>();
        for (int i = 0; i < 9; ++i) {
            for (int j = 0; j < 9; ++j) {
                char number = board[i][j];
                if (number != '.') {
                    if (!seen.add(number + " in row " + i) ||
                            !seen.add(number + " in column " + j) ||
                            !seen.add(number + " in block " + i / 3 + "-" + j / 3)) {
                        return false;
                    }
                }
            }
        }
        return true;
    }
}