LeetCode-in-Go

36. Valid Sudoku

Medium

Determine if a 9 x 9 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 nine 3 x 3 sub-boxes of the grid must contain the digits 1-9 without repetition.

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.

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

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

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.

Constraints:

• board.length == 9
• board[i].length == 9
• board[i][j] is a digit 1-9 or '.'.

Solution

type Solution struct {
	j1 int
	i1 [9]int
	b1 [9]int
}

func isValidSudoku(board [][]byte) bool {
	s := &Solution{}
	for i := 0; i < 9; i++ {
		for j := 0; j < 9; j++ {
			if !s.checkValid(board, i, j) {
				return false
			}
		}
	}
	return true
}

func (s *Solution) checkValid(board [][]byte, i, j int) bool {
	if j == 0 {
		s.j1 = 0
	}
	if board[i][j] == '.' {
		return true
	}
	val := int(board[i][j] - '0')
	if s.j1 == (s.j1 | (1 << (val - 1))) {
		return false
	}
	s.j1 |= 1 << (val - 1)
	if s.i1[j] == (s.i1[j] | (1 << (val - 1))) {
		return false
	}
	s.i1[j] |= 1 << (val - 1)
	b := (i/3)*3 + j/3
	if s.b1[b] == (s.b1[b] | (1 << (val - 1))) {
		return false
	}
	s.b1[b] |= 1 << (val - 1)
	return true
}

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