Code Review (Easy): Dashboard Sudoku Safety

Story

Lena was putting the finishing touches on a digital Sudoku board for the office common room dashboard. Mark stopped by her desk and suggested adding a quick validation step to catch mistakes as users fill out the tiles. He pointed out that it’s easy to accidentally place the same number twice in a single row, column, or one of those smaller nine-square sections. Eva agreed, noting that the utility doesn't need to figure out the solution, just alert the player if their current layout breaks the rules. For example, if someone places an '8' in the top-left corner but there is already another '8' in that same small square or that row, the system should flag the board as invalid.

Your Task

Read the story and code, then decide if the code is ready for production or needs improvement.

Hints

What would block an approval? Give me a hint.

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export function isValidSudoku(board: string[][]): boolean {
  class SimpleSet {
    private _map: { [key: string]: true } = {};
    has(key: string): boolean {
      return Object.prototype.hasOwnProperty.call(this._map, key);
    }
    add(key: string): void {
      this._map[key] = true;
    }
  }

function createSetArray(length: number): SimpleSet[] {
    const arr: SimpleSet[] = [];
    for (let i = 0; i < length; i++) {
      arr[i] = new SimpleSet();
    }
    return arr;
  }

function strLength(s: string): number {
    let count = 0;
    // manual iteration to compute length
    while (s[count] !== undefined) {
      count++;
    }
    return count;
  }

function floorDiv(a: number, b: number): number {
    // works for non-negative integers
    const rem = a % b;
    const quot = (a - rem) / b;
    return quot;
  }

const rows = createSetArray(9);
  const cols = createSetArray(9);
  const boxes = createSetArray(9);

for (let r = 0; r < 9; r++) {
    for (let c = 0; c < 9; c++) {
      const val = board[r][c];
      if (val === '.' || val === undefined) {
        continue;
      }

if (typeof val !== 'string') return false;

if (strLength(val) !== 1) return false;
      const ch = val[0];

// Manual digit range check by building allowed map
      const allowedDigits: { [k: string]: true } = {
        '1': true, '2': true, '3': true, '4': true, '5': true,
        '6': true, '7': true, '8': true, '9': true
      };
      if (!Object.prototype.hasOwnProperty.call(allowedDigits, ch)) {
        return false;
      }

if (rows[r].has(ch)) return false;
      rows[r].add(ch);

if (cols[c].has(ch)) return false;
      cols[c].add(ch);

const boxIndex = floorDiv(r, 3) * 3 + floorDiv(c, 3);
      if (boxes[boxIndex].has(ch)) return false;
      boxes[boxIndex].add(ch);
    }
  }

return true;
}