Added TernarySearch Function

Search/TernarySearch.js

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+/* Ternary search is similar to binary search but it divide the sorted array
+ * into three parts and determine which part the key lies in. The array will
+ * be divided into three intervals by using two middle points, mid1 and mid2.
+ * The value of the key will first compared with the two mid points, the value
+ * will be returned if there is a match. Then, if the value of the key is less
+ * than mid1, narrow the interval to the first part. Else, if the value of the
+ * key is greater than mid2, narrow the interval to the third part. Otherwise,
+ * narrow the interval to the middle part. Repeat the steps until the value is
+ * found or the interval is empty(value not found after checking all elements).
+ *
+ * Reference: https://www.geeksforgeeks.org/ternary-search/
+ */
+
+/*
+*  Doctests
+*
+*  > ternarySearchRecursive([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], 3)
+*  2
+*  > ternarySearchIterative([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], 8)
+*  7
+*  > ternarySearchRecursive([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], 0)
+*  -1
+*  > ternarySearchIterative([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], 12)
+*  -1
+*  > ternarySearchRecursive(["Ali", "Cathrynli", "Josuke", "Thomas"], "Cathrynli")
+*  1
+*  > ternarySearchRecursive(["Ali", "Cathrynli", "Josuke", "Thomas"], "Josuke")
+*  2
+*  > ternarySearchRecursive(["Ali", "Cathrynli", "Josuke", "Thomas"], "Angela")
+*  -1
+*/
+
+function ternarySearchRecursive (arr, key, low = 0, high = arr.length - 1) {
+  if (high >= low) {
+    // find the mid1 and mid2
+    const mid1 = Math.floor(low + (high - low) / 3)
+    const mid2 = Math.floor(high - (high - low) / 3)
+
+    // check if key is found at any mid
+    if (arr[mid1] === key) {
+      // return index of key if found
+      return mid1
+    }
+    if (arr[mid2] === key) {
+      // return index of key if found
+      return mid2
+    }
+
+    // since the key is not found at mid,
+    // check in which region it is present
+    // and repeat the Search operation
+    // in that region
+    if (key < arr[mid1]) {
+      // the key lies in between low and mid1
+      return ternarySearchRecursive(arr, key, low, mid1 - 1)
+    } else if (key > arr[mid2]) {
+      // the key lies in between mid2 and high
+      return ternarySearchRecursive(arr, key, mid2 + 1, high)
+    } else {
+      // the key lies in between mid1 and mid2
+      return ternarySearchRecursive(arr, key, mid1 + 1, mid2 - 1)
+    }
+  } else {
+    // if low > high => we have searched the whole array without finding the item
+    return -1
+  }
+}
+function ternarySearchIterative (arr, key, low = 0, high = arr.length - 1) {
+  while (high >= low) {
+    // find the mid1 and mid2
+    const mid1 = Math.floor(low + (high - low) / 3)
+    const mid2 = Math.floor(high - (high - low) / 3)
+
+    // check if key is found at any mid
+    if (arr[mid1] === key) {
+      // return index of key if found
+      return mid1
+    }
+    if (arr[mid2] === key) {
+      // return index of key if found
+      return mid2
+    }
+
+    // since the key is not found at mid,
+    // check in which region it is present
+    // and repeat the Search operation
+    // in that region
+    if (key < arr[mid1]) {
+      // the key lies in between low and mid1
+      high = mid1 - 1
+    } else if (key > arr[mid2]) {
+      // the key lies in between mid2 and high
+      low = mid2 + 1
+    } else {
+      // the key lies in between mid1 and mid2
+      low = mid1 + 1
+      high = mid2 - 1
+    }
+  }
+  // the key was not found
+  return -1
+}
+
+export { ternarySearchRecursive, ternarySearchIterative }

Search/test/TernarySearch.test.js

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+import { ternarySearchRecursive, ternarySearchIterative } from '../TernarySearch'
+
+test('should return the index of a number in an array of numbers:', () => {
+  const indexNumber = ternarySearchRecursive([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], 3)
+  expect(indexNumber).toBe(2)
+})
+
+test('should return the index of a number in an array of numbers:', () => {
+  const indexNumber = ternarySearchIterative([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], 8)
+  expect(indexNumber).toBe(7)
+})
+
+test('should return the index of a number in an array of numbers:', () => {
+  const indexNumber = ternarySearchRecursive([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], 0)
+  expect(indexNumber).toBe(-1)
+})
+
+test('should return the index of a number in an array of numbers:', () => {
+  const indexNumber = ternarySearchIterative([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], 12)
+  expect(indexNumber).toBe(-1)
+})
+
+test('should return the index of a string in an array of strings:', () => {
+  const indexNumber = ternarySearchRecursive(['Ali', 'Cathrynli', 'Josuke', 'Thomas'], 'Cathrynli')
+  expect(indexNumber).toBe(1)
+})
+
+test('should return the index of a string in an array of strings:', () => {
+  const indexNumber = ternarySearchRecursive(['Ali', 'Cathrynli', 'Josuke', 'Thomas'], 'Josuke')
+  expect(indexNumber).toBe(2)
+})
+
+test('should return the index of a string in an array of strings:', () => {
+  const indexNumber = ternarySearchRecursive(['Ali', 'Cathrynli', 'Josuke', 'Thomas'], 'Angela')
+  expect(indexNumber).toBe(-1)
+})