36. Valid Sudoku

1function isValidSudoku(board: string[][]): boolean {
2  const rows = Array.from({ length: 9 }, () => new Set<string>());
3  const cols = Array.from({ length: 9 }, () => new Set<string>());
4  const boxes = Array.from({ length: 9 }, () => new Set<string>());
5  for (let r = 0; r < 9; r++)
6    for (let c = 0; c < 9; c++) {
7      const d = board[r][c];
8      if (d === ".") continue;
9      const b = Math.floor(r / 3) * 3 + Math.floor(c / 3);
10      if (rows[r].has(d) || cols[c].has(d) || boxes[b].has(d)) return false;
11      rows[r].add(d); cols[c].add(d); boxes[b].add(d);
12    }
13  return true;
14}

27 empty sets: 9 rows, 9 columns, 9 boxes.

Space: play/pause · ←/→: step