From e3d90576a92e372dbcbb6109571774818bfb0b4c Mon Sep 17 00:00:00 2001
From: GohJunLe <108907711+GohJunLe@users.noreply.github.com>
Date: Tue, 9 Aug 2022 08:36:48 +0800
Subject: [PATCH] Add exponential search

---
 .../__test__/exponentialSearch.test.js        | 35 ++++++++++
 .../exponential-search/exponentialSearch.js   | 67 +++++++++++++++++++
 2 files changed, 102 insertions(+)
 create mode 100644 src/algorithms/search/exponential-search/__test__/exponentialSearch.test.js
 create mode 100644 src/algorithms/search/exponential-search/exponentialSearch.js

diff --git a/src/algorithms/search/exponential-search/__test__/exponentialSearch.test.js b/src/algorithms/search/exponential-search/__test__/exponentialSearch.test.js
new file mode 100644
index 00000000..0816af2b
--- /dev/null
+++ b/src/algorithms/search/exponential-search/__test__/exponentialSearch.test.js
@@ -0,0 +1,35 @@
+import exponentialSearch from '../exponentialSearch';
+
+describe('exponentialSearch', () => {
+  it('should search number in sorted array', () => {
+    expect(exponentialSearch([], 1)).toBe(-1);
+    expect(exponentialSearch([1], 1)).toBe(0);
+    expect(exponentialSearch([1, 2], 1)).toBe(0);
+    expect(exponentialSearch([1, 2], 2)).toBe(1);
+    expect(exponentialSearch([1, 5, 10, 12], 1)).toBe(0);
+    expect(exponentialSearch([1, 5, 10, 12, 14, 17, 22, 100], 17)).toBe(5);
+    expect(exponentialSearch([1, 5, 10, 12, 14, 17, 22, 100], 1)).toBe(0);
+    expect(exponentialSearch([1, 5, 10, 12, 14, 17, 22, 100], 100)).toBe(7);
+    expect(exponentialSearch([1, 5, 10, 12, 14, 17, 22, 100], 0)).toBe(-1);
+  });
+
+  it('should search object in sorted array', () => {
+    const sortedArrayOfObjects = [
+      { key: 1, value: 'value1' },
+      { key: 2, value: 'value2' },
+      { key: 3, value: 'value3' },
+      { key: 4, value: 'value4' },
+    ];
+
+    const comparator = (a, b) => {
+      if (a.key === b.key) return 0;
+      return a.key < b.key ? -1 : 1;
+    };
+
+    expect(exponentialSearch([], { key: 1 }, comparator)).toBe(-1);
+    expect(exponentialSearch(sortedArrayOfObjects, { key: 4 }, comparator)).toBe(3);
+    expect(exponentialSearch(sortedArrayOfObjects, { key: 1 }, comparator)).toBe(0);
+    expect(exponentialSearch(sortedArrayOfObjects, { key: 2 }, comparator)).toBe(1);
+    expect(exponentialSearch(sortedArrayOfObjects, { key: 3 }, comparator)).toBe(2);
+  });
+});
diff --git a/src/algorithms/search/exponential-search/exponentialSearch.js b/src/algorithms/search/exponential-search/exponentialSearch.js
new file mode 100644
index 00000000..b9c69693
--- /dev/null
+++ b/src/algorithms/search/exponential-search/exponentialSearch.js
@@ -0,0 +1,67 @@
+import Comparator from '../../../utils/comparator/Comparator';
+
+/**
+ * Binary search implementation.
+ *
+ * @param {*[]} sortedArray
+ * @param {*} startIndex
+ * @param {*} endIndex
+ * @param {*} seekElement
+ * @param {function(a, b)} [comparatorCallback]
+ * @return {number}
+ */
+
+function binarySearch(sortedArray, startIndex, endIndex, seekElement, comparatorCallback)
+{
+    const comparator = new Comparator(comparatorCallback);
+    
+    if (endIndex >= startIndex)
+    {
+        const middleIndex = startIndex + Math.floor((endIndex - startIndex) / 2);
+   
+        // If the element is present at the middle itself
+        if (comparator.equal(sortedArray[middleIndex], seekElement))
+            return middleIndex;
+   
+        // If element is smaller than middleIndex, then it can only be  present n left subarray
+        if (comparator.greaterThan(sortedArray[middleIndex], seekElement)){
+            return binarySearch(sortedArray, startIndex, middleIndex - 1, seekElement, comparatorCallback);
+        }else{
+        // Else the element can only be present in right subarray
+        return binarySearch(sortedArray, middleIndex + 1, endIndex, seekElement, comparatorCallback);
+        }
+        
+    }
+
+    // We reach here when element is not present in array
+    return -1;
+}
+
+/**
+ * Exponential search implementation.
+ *
+ * @param {*[]} sortedArray
+ * @param {*} seekElement
+ * @param {function(a, b)} [comparatorCallback]
+ * @return {number}
+ */
+
+export default function exponentialSearch(sortedArray, seekElement, comparatorCallback)
+{
+    const comparator = new Comparator(comparatorCallback);
+    const length = sortedArray.length;
+       
+    // If element is present at first location itself
+    if(sortedArray.length != 0){
+        if (comparator.equal(sortedArray[0], seekElement))
+        return 0;
+    }
+   
+    // Find range for binary search by repeated doubling
+    let range = 1;
+    while (range < length && comparator.lessThanOrEqual(sortedArray[range], seekElement))
+        range = range * 2;
+   
+    // Call binary search for the found range.
+    return binarySearch(sortedArray, range/2, Math.min(range, length - 1), seekElement, comparatorCallback);
+}
\ No newline at end of file