Solved (JS): Determine if a 9x9 Sudoku board is valid

readme.md

Valid Sudoku

Determine if a 9x9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:

1. Each row must contain the digits 1-9 without repetition.
2. Each column must contain the digits 1-9 without repetition.
3. 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 '.'.

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.

is-valid-sudoku.js

const isValidSudoku = (board) => {
    const obj = { 
        rows: {}, // 9 rows, each containing 9 cells across
        columns: {}, // 9 columns, each containing 9 cells down
        blocks: {}, // 9 blocks, each containing 3x3 cells inside
    };
    
    let isValid = true;
    
    loop1:
    for (let r = 0; r < board.length; r++) {
        
        loop2:
        for (let c = 0; c < board[r].length; c++) {
            
            const cellValue = board[r][c];
            
            if (cellValue === '.') {
                continue;
            }
            
            // 1: validate rows
            if (!obj.rows.hasOwnProperty(r)) {
                obj.rows[r] = {};
            }
            
            if (obj.rows[r].hasOwnProperty(cellValue)) {
                isValid = false;
                break loop1;
            } else {
                obj.rows[r][cellValue] = null;   
            }
            
            // 2: validate columns
            if (!obj.columns.hasOwnProperty(c)) {
                obj.columns[c] = {};
            }
            
            if (obj.columns[c].hasOwnProperty(cellValue)) {
                isValid = false;
                break loop1;
            } else {
                obj.columns[c][cellValue] = null;   
            }
            
            // 3: validate grid
            const b = getBlockNumber(r, c);
            
            if (!obj.blocks.hasOwnProperty(b)) {
                obj.blocks[b] = {};
            }
            
            if (obj.blocks[b].hasOwnProperty(cellValue)) {
                isValid = false;
                break loop1;
            } else {
                obj.blocks[b][cellValue] = null;   
            }
        }
    }
    
    return isValid;
};

// if row = 8 & column = 5
// then quotients = 2, 1
// therefore blockNumber = 8
const getBlockNumber = (row, column) => {
    const rowQuotient = parseInt(row / 3, 10);
    const columnQuotient = parseInt(column / 3, 10);
    
    let blockNumber;

    switch(`${rowQuotient}${columnQuotient}`) {
        case '00': blockNumber = 0; break;
        case '01': blockNumber = 1; break;
        case '02': blockNumber = 2; break;
        case '10': blockNumber = 3; break;
        case '11': blockNumber = 4; break;
        case '12': blockNumber = 5; break;
        case '20': blockNumber = 6; break;
        case '21': blockNumber = 7; break;
        case '22': blockNumber = 8; break;
    };

    return blockNumber;
};