InterpolationSearch and test cases

src/main/scala/Search/InterpolationSearch.scala

@@ -0,0 +1,45 @@
+package Search
+
+/*
+  An implementation of the Interpolation algorithm to search an
+  element in a sorted list of uniformly distributed values.
+  Interpolation algorithm is based on the binary search algorithm but instead of going to
+  the middle element, it checks elements closer to the edges.
+ */
+object InterpolationSearch {
+  /**
+   *
+   * @param arr  a sequence of uniformly distributed values
+   * @param elem an integer to search for in @arr
+   * @return index of the @elem else -1
+   */
+  def interpolationSearch(arr: List[Int], elem: Int): Int = {
+    var low = 0
+    var high = arr.size - 1
+
+    while (low <= high && elem>=arr(low) && elem <=arr(high)) {
+      //The interpolation formula that decides the next position keeping the uniform distribution in mind.
+      var pos = low + ((elem - arr(low)) * (high - low) / (arr(high) - arr(low)))
+      //Target index found
+      if (arr(pos) == elem) {
+        return pos
+      }
+      //If target is bigger, search right part of list.
+      else if (arr(pos) < elem) {
+        low = pos + 1
+      }
+      //If target is lower, search left part of list.
+      else {
+        high = pos - 1
+      }
+    }
+    //If element is not found.
+    -1
+  }
+  def main(args:Array[String]):Unit ={
+    val arr = List(10, 12, 13, 16, 18, 19, 20, 21,
+      22, 23, 24, 33, 35, 42, 47)
+
+    println(interpolationSearch(arr,48))
+  }
+}

src/test/scala/Search/InterpolationSearchSpec.scala

@@ -0,0 +1,17 @@
+package Search
+
+import org.scalatest.FlatSpec
+
+class InterpolationSearchSpec extends FlatSpec {
+  "An Interpolation Search" should "return the index of an element in an array" in{
+    val l = List.range(1,10)
+    assert(InterpolationSearch.interpolationSearch(l,2)===1)
+    assert(InterpolationSearch.interpolationSearch(l,9)===8)
+  }
+
+  it should "return -1 if the element is not found in the list" in{
+    val l = List(10, 12, 13, 16, 18, 19, 20, 21,
+      22, 23, 24, 33, 35, 42, 47)
+    assert(InterpolationSearch.interpolationSearch(l,48) === -1)
+  }
+}