LeetCode in Kotlin

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

class Solution {
    private var j1 = 0
    private val i1 = IntArray(9)
    private val b1 = IntArray(9)

    fun isValidSudoku(board: Array<CharArray>): Boolean {
        for (i in 0..8) {
            for (j in 0..8) {
                val res = checkValid(board, i, j)
                if (!res) {
                    return false
                }
            }
        }
        return true
    }

    private fun checkValid(board: Array<CharArray>, i: Int, j: Int): Boolean {
        if (j == 0) {
            j1 = 0
        }
        if (board[i][j] == '.') {
            return true
        }
        val `val` = board[i][j] - '0'
        if (j1 == j1 or (1 shl `val` - 1)) {
            return false
        }
        j1 = j1 or (1 shl `val` - 1)
        if (i1[j] == i1[j] or (1 shl `val` - 1)) {
            return false
        }
        i1[j] = i1[j] or (1 shl `val` - 1)
        val b = i / 3 * 3 + j / 3
        if (b1[b] == b1[b] or (1 shl `val` - 1)) {
            return false
        }
        b1[b] = b1[b] or (1 shl `val` - 1)
        return true
    }
}

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