chore: Add Interpolation Search (#308)

Author: hariprasadraja

searches/interpolation_search.go/interpolation_search_test.go

@@ -0,0 +1,31 @@
+package interpolationsearch
+
+import "testing"
+
+type searchTest struct {
+	data     []int
+	key      int
+	expected int
+	name     string
+}
+
+var searchTests = []searchTest{
+	//Sanity
+	{[]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 1, 0, "Sanity"},
+	{[]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 5, 4, "Sanity"},
+	{[]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 10, 9, "Sanity"},
+	//Absent
+	{[]int{1, 4, 5, 6, 7, 10}, -25, -1, "Absent"},
+	{[]int{1, 4, 5, 6, 7, 10}, 25, -1, "Absent"},
+	//Empty slice
+	{[]int{}, 2, -1, "Empty"},
+}
+
+func TestInterpolationSearch(t *testing.T) {
+	for _, test := range searchTests {
+		actual := InterpolationSearch(test.data, test.key)
+		if actual != test.expected {
+			t.Errorf("test %s failed", test.name)
+		}
+	}
+}

searches/interpolation_search.go/interpolationsearch.go

@@ -0,0 +1,51 @@
+package interpolationsearch
+
+/*
+InterpolationSearch searches for the entity in the given sortedData.
+if the entity is present, it will return the index of the entity, if not -1 will be returned.
+see: https://en.wikipedia.org/wiki/Interpolation_search
+Complexity
+	Worst: O(N)
+	Average: O(log(log(N))  if the elements are uniformly distributed
+	Best: O(1)
+
+Example
+		fmt.Println(InterpolationSearch([]int{1, 2, 9, 20, 31, 45, 63, 70, 100},100))
+*/
+func InterpolationSearch(sortedData []int, guess int) int {
+	if len(sortedData) == 0 {
+		return -1
+	}
+
+	var (
+		low, high       = 0, len(sortedData) - 1
+		lowVal, highVal = sortedData[low], sortedData[high]
+	)
+
+	for lowVal != highVal && (lowVal <= guess) && (guess <= highVal) {
+		mid := low + int(float64(float64((guess-lowVal)*(high-low))/float64(highVal-lowVal)))
+
+		// if guess is found, array can also have duplicate values, so scan backwards and find the first index
+		if sortedData[mid] == guess {
+			for mid > 0 && sortedData[mid-1] == guess {
+				mid--
+			}
+			return mid
+
+		}
+
+		// adjust our guess and continue
+		if sortedData[mid] > guess {
+			high, highVal = mid-1, sortedData[high]
+
+		} else {
+			low, lowVal = mid+1, sortedData[low]
+		}
+
+	}
+
+	if guess == lowVal {
+		return low
+	}
+	return -1
+}