36.valid-sudoku.java

/*
 * @lc app=leetcode id=36 lang=java
 *
 * [36] Valid Sudoku
 *
 * https://leetcode.com/problems/valid-sudoku/description/
 *
 * algorithms
 * Medium (41.89%)
 * Total Accepted:    225.5K
 * Total Submissions: 531.1K
 * Testcase Example:  '[["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"]]'
 *
 * Determine if a 9x9 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 9 3x3 sub-boxes of the grid must contain the digits 1-9 without
 * repetition.
 *
 *
 *
 * A partially filled sudoku which is valid.
 *
 * The Sudoku board could be partially filled, where empty cells are filled
 * with the character '.'.
 *
 * Example 1:
 *
 *
 * Input:
 * [
 * ⁠ ["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:
 * [
 * ["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.
 *
 *
 * 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.
 * The given board contain only digits 1-9 and the character '.'.
 * The given board size is always 9x9.
 *
 *
 */
class Solution {
  public boolean isValidSudoku(char[][] board) {
    if (board == null || board.length != 9 || board[0].length != 9) {
      return false;
    }

    boolean[][] rows = new boolean[9][9];
    boolean[][] cols = new boolean[9][9];
    boolean[][] boxs = new boolean[9][9];

    for (int i = 0; i < 9; i++) {
      for (int j = 0; j < 9; j++) {
        if ('1' <= board[i][j] && board[i][j] <= '9') {
          int k = (i / 3) * 3 + j / 3;
          int num = board[i][j] - '1';
          if (rows[i][num] || cols[j][num] || boxs[k][num]) {
            return false;
          }
          rows[i][num] = cols[j][num] = boxs[k][num] = true;
        }
      }
    }

    return true;
  }
}