solutions/0036-valid-sudoku.js

/**
 * 36. Valid Sudoku
 * https://leetcode.com/problems/valid-sudoku/
 * Difficulty: Medium
 *
 * 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.
 *
 * The Sudoku board could be partially filled, where empty cells are filled with the character '.'.
 */

/**
 * @param {character[][]} board
 * @return {boolean}
 */
var isValidSudoku = function(board) {
  const rows = new Array(9).fill().map(() => new Set());
  const columns = new Array(9).fill().map(() => new Set());
  const boxes = new Array(9).fill().map(() => new Set());

  for (let i = 0; i < 9; i++) {
    for (let j = 0; j < 9; j++) {
      const value = board[i][j];
      const k = Math.floor(i / 3) * 3 + Math.floor(j / 3);
      const options = [rows[i], columns[j], boxes[k]];

      if (options.some(option => option.has(value))) return false;
      if (value !== '.') options.forEach(option => option.add(value));
    }
  }

  return true;
};