Created
April 18, 2012 21:45
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Scala bible's implementation of an N-Queens solver.
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| def queens(n: Int): List[List[(Int, Int)]] = { | |
| def placeQueens(k: Int): List[List[(Int, Int)]] = | |
| if (k == 0) | |
| List(List()) | |
| else | |
| for { | |
| queens <- placeQueens(k - 1) | |
| column <- 1 to n | |
| queen = (k, column) | |
| if isSafe(queen, queens) | |
| } yield queen :: queens | |
| placeQueens(n) | |
| } | |
| def isSafe(queen: (Int, Int), queens: List[(Int, Int)]) = | |
| queens forall (q => !inCheck(queen, q)) | |
| def inCheck(q1: (Int, Int), q2: (Int, Int)) = | |
| q1._1 == q2._1 || // same row | |
| q1._2 == q2._2 || // same column | |
| (q1._1 - q2._1).abs == (q1._2 - q2._2).abs // on diagonal |
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