fix: find interpolation search keys in constant arrays

Author: pralav-25

Search/InterpolationSearch.js

@@ -18,6 +18,11 @@ export function interpolationSearch(arr, key) {
 
   // Because the array is sorted the key must be between low and high
   while (low <= high && key >= arr[low] && key <= arr[high]) {
+    // Equal endpoints mean every remaining element matches the key.
+    if (arr[low] === arr[high]) {
+      return low
+    }
+
     delta = (key - arr[low]) / (arr[high] - arr[low])
     position = low + Math.floor((high - low) * delta)
 

Search/test/InterpolationSearch.test.js

@@ -1,5 +1,17 @@
 import { interpolationSearch } from '../InterpolationSearch'
 
+test.each([
+  [[7], 7, 0],
+  [[7, 7, 7], 7, 0],
+  [[-4, -4, -4], -4, 0],
+  [[0, 0], 0, 0],
+  [[7], 6, -1],
+  [[7, 7, 7], 8, -1],
+  [[], 7, -1]
+])('interpolationSearch(%j, %s) => %s', (array, key, expected) => {
+  expect(interpolationSearch(array, key)).toBe(expected)
+})
+
 test('interpolationSearch([2, 6, 8, 14, 122, 169], 144) => -1', () => {
   const array = [2, 6, 8, 14, 122, 169]
   const key = 144