g0001_0100.s0037_sudoku_solver.Solution.kt Maven / Gradle / Ivy
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Kotlin-based LeetCode algorithm problem solutions, regularly updated
package g0001_0100.s0037_sudoku_solver
// #Hard #Array #Matrix #Backtracking #2022_09_18_Time_294_ms_(79.69%)_Space_34.8_MB_(93.75%)
class Solution {
private val emptyCells: MutableList = ArrayList()
private val rows = IntArray(9)
private val cols = IntArray(9)
private val boxes = IntArray(9)
fun solveSudoku(board: Array) {
for (r in 0..8) {
for (c in 0..8) {
if (board[r][c] == '.') {
emptyCells.add(intArrayOf(r, c))
} else {
val `val` = board[r][c] - '0'
val boxPos = r / 3 * 3 + c / 3
rows[r] = rows[r] or (1 shl `val`)
cols[c] = cols[c] or (1 shl `val`)
boxes[boxPos] = boxes[boxPos] or (1 shl `val`)
}
}
}
backtracking(board, 0)
}
private fun backtracking(board: Array, i: Int): Boolean {
// Check if we filled all empty cells?
if (i == emptyCells.size) {
return true
}
val r = emptyCells[i][0]
val c = emptyCells[i][1]
val boxPos = r / 3 * 3 + c / 3
for (`val` in 1..9) {
// skip if that value is existed!
if (hasBit(rows[r], `val`) || hasBit(cols[c], `val`) || hasBit(boxes[boxPos], `val`)) {
continue
}
board[r][c] = ('0' + `val`)
// backup old values
val oldRow = rows[r]
val oldCol = cols[c]
val oldBox = boxes[boxPos]
rows[r] = rows[r] or (1 shl `val`)
cols[c] = cols[c] or (1 shl `val`)
boxes[boxPos] = boxes[boxPos] or (1 shl `val`)
if (backtracking(board, i + 1)) {
return true
}
rows[r] = oldRow
cols[c] = oldCol
boxes[boxPos] = oldBox
}
return false
}
private fun hasBit(x: Int, k: Int): Boolean {
return x shr k and 1 == 1
}
}