Finds the elements shared by 2 lists, FP style, recursively
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object Intersect extends App{ | |
import scala.annotation.tailrec | |
// finds the elements shared by 2 lists, FP style, recursively | |
// O(n log n) | |
@tailrec | |
def scan(x: List[Int], y: List[Int], out: List[Int] = List.empty[Int]): List[Int] = | |
(x, y) match { | |
case (xhead :: xtail, yhead :: ytail) => | |
if (xhead == yhead) scan(xtail, ytail, xhead :: out) | |
else if (xhead < yhead) scan(xtail, y, out) | |
else scan(x, ytail, out) | |
case _ => out | |
} | |
def intersect(x: List[Int], y: List[Int]): List[Int] = | |
scan(x.sorted, y.sorted).reverse | |
val li1 = List(3, 6, 7, 1, 2) | |
val li2 = List(4, 5, 1, 6, 3, 20, 0) | |
println(intersect(li1, li2)) | |
// sanity check, here we use Scala's inbuilt Set functionality | |
println(li1.toSet.intersect(li2.toSet)) | |
// sanity check, and in built intersect | |
println(li1.intersect(li2)) | |
// all the above show that common elements are 1, 3 and 6 | |
} |
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