Scala By Example Chapter 10 Solutions - Exercise 10.1.1

Exercise10.1.1 Write the function isSafe.

	object NQueensProblem {
	def queens(n: Int): List[List[Int]] = {
	def placeQueens(k: Int): List[List[Int]] =
	if (k == 0) List(List())
	else for { queens <- placeQueens(k - 1)
	column <- List.range(1, n + 1)
	if isSafe(column, queens, 1)} yield column :: queens
	placeQueens(n)
	}
	def isSafe(col: Int, queens: List[Int], delta: Int): Boolean = queens match {
	case Nil => true
	case x :: xs => col != x && col != x - delta && col != x + delta &&
	isSafe(col, xs, delta + 1)
	}
	def main(args: Array[String]) {
	println ("Solving nqueens: ")
	val x = queens(8)
	println("Number of solutions: " + x.length)
	println(x)
	}
	}

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