DSA & System Design

Valid Sudoku

MediumMatrix and Grid SimulationHash Maps and Sets

You are given a partially filled 9 x 9 Sudoku board as a grid of strings. Each cell is either a digit "1" to "9" or "." for an empty cell. Return true if the board is valid so far, meaning:

  • each row contains no digit more than once,
  • each column contains no digit more than once,
  • each of the nine 3 x 3 boxes (the ones that start at rows and columns 0, 3 and 6) contains no digit more than once.

Only the filled cells are checked. A valid board does not have to be solvable.

Constraints

  • The board has exactly 9 rows and 9 columns.
  • Every cell is "." or a digit from "1" to "9".

Examples

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

The well-known partial puzzle breaks no row, column or box rule. It does not need to be solvable, only consistent.

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

Putting an 8 in the top-left corner repeats the 8 of row 3 in the same column, and the 8 in row 2 in the same box.

Example 3

Input: board = [["5",".",".",".",".",".",".",".","."],[".","3",".",".",".",".",".",".","."],[".",".","5",".",".",".",".",".","."],[".",".",".",".",".",".",".",".","."],[".",".",".",".",".",".",".",".","."],[".",".",".",".",".",".",".",".","."],[".",".",".",".",".",".",".",".","."],[".",".",".",".",".",".",".",".","."],[".",".",".",".",".",".",".",".","."]]
Output: false

No row or column repeats, but both 5s sit in the top-left 3 x 3 box.

JavaScript you'll use: Map and Set Arrays: create, read, update

/**
 * @param {string[][]} board
 * @return {boolean}
 */
function isValidSudoku(board) {
  
}

Ctrl/⌘ + ' runs the examples, Ctrl/⌘ + Enter submits. Use console.log freely: output shows under Console. In the editor, press Esc then Tab to move focus out.