Validate a Partially Filled Sudoku Board
Company: Verkada
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Technical Screen
# Validate a Partially Filled Sudoku Board
You are given a partially filled `9 x 9` Sudoku board. Each cell is either a digit from `1` through `9` or `.` for an empty cell.
Implement:
```text
isValidSudoku(board) -> boolean
```
Return `true` exactly when the filled cells satisfy all three rules:
- No digit appears more than once in any row.
- No digit appears more than once in any column.
- No digit appears more than once in any of the nine `3 x 3` boxes.
Only validate the cells already filled. The board does not need to be solvable or complete. `board` is represented as a list of nine strings, each containing exactly nine valid cell characters.
## Constraints
- `board.length == 9`
- `board[i].length == 9`
- Every character is `.` or a digit from `1` through `9`.
## Examples
### Example 1
```text
board = [
"53..7....",
"6..195...",
".98....6.",
"8...6...3",
"4..8.3..1",
"7...2...6",
".6....28.",
"...419..5",
"....8..79"
]
output = true
```
No filled digit is repeated within a row, column, or box.
### Example 2
```text
board = [
"83..7....",
"6..195...",
".98....6.",
"8...6...3",
"4..8.3..1",
"7...2...6",
".6....28.",
"...419..5",
"....8..79"
]
output = false
```
The digit `8` appears twice in the top-left `3 x 3` box.
Overview: Validate a partially filled Sudoku board by checking every row, column, and three-by-three box for duplicate digits. The prompt distinguishes validity from solvability and defines empty-cell and fixed-board representations for a deterministic Boolean result.
Read the full Verkada Software Engineer interview experience this question came from
Implement isValidSudoku(board) for a 9 x 9 board represented by nine strings of nine characters. Each character is '.' or a digit '1' through '9'. Return true exactly when no filled digit is repeated in any row, column, or 3 x 3 box. Validate only filled cells; the board need not be complete or solvable.
Constraints
- board.length == 9
- board[i].length == 9
- Every character is '.' or a digit from '1' through '9'.
- Only filled cells are validated; completeness and solvability are not required.
Examples
Input: (['.........', '.........', '.........', '.........', '.........', '.........', '.........', '.........', '.........'],)
Expected Output: True
Explanation: An entirely empty board has no duplicate filled digit.
Input: (['53..7....', '6..195...', '.98....6.', '8...6...3', '4..8.3..1', '7...2...6', '.6....28.', '...419..5', '....8..79'],)
Expected Output: True
Explanation: The first source example satisfies all three uniqueness rules.
Hints
- Track seen digits separately for each row, each column, and each box.
- Map cell (row, column) to box (row // 3) * 3 + column // 3.