diff --git a/Search/SentinelSearch.js b/Search/SentinelSearch.js
new file mode 100644
index 0000000000..c6d14714a4
--- /dev/null
+++ b/Search/SentinelSearch.js
@@ -0,0 +1,35 @@
+/**
+ * @description Sentinel linear search is a variation of the standard linear search algorithm used to
+ * find a target value in an array or list. The basic idea behind this algorithm is to add a
+ * sentinel value at the end of the array which is equal to the target value we are looking for.
+ * This helps to avoid checking the array boundary condition during each iteration of the loop,
+ * as the sentinel value acts as a stopper for the loop.
+ *
+ * @param {number[]} array - sorted list of numbers
+ * @param {number} target - target number to search for
+ * @return {number | null} - index of the target number in the list, or null if not found
+ * @see [SentinelSearch](https://www.geeksforgeeks.org/sentinel-linear-search/)
+ * @example sentinelSearch([1,2,3], 2) => 1
+ * @example sentinelSearch([4,5,6], 2) => null
+ * @complexity_analysis
+ * Time Complexity : O(n)
+ * Auxiliary Space: O(1)
+ */
+
+export const sentinelSearch = (array, target) => {
+ const arrayLength = array.length
+ if (arrayLength === 0) return null
+
+ // Element to be searched is placed at the last index
+ const last = array[arrayLength - 1]
+ array[arrayLength - 1] = target
+
+ let index = 0
+ while (array[index] !== target) index++
+
+ // Put the last element back
+ array[arrayLength - 1] = last
+
+ if (index < arrayLength - 1 || array[arrayLength - 1] === target) return index
+ return null
+}
diff --git a/Search/TernarySearch.js b/Search/TernarySearch.js
index ea0d049341..1e0c568a61 100644
--- a/Search/TernarySearch.js
+++ b/Search/TernarySearch.js
@@ -12,38 +12,33 @@
*/
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)
+ // if low > high => we have searched the whole array without finding the item
+ if (low > high) return -1
- // 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
- }
+ // find the mid1 and mid2
+ const mid1 = Math.floor(low + (high - low) / 3)
+ const mid2 = Math.floor(high - (high - low) / 3)
- // 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)
- }
+ // check if key is found at any mid
+ // return index of key if found
+ if (arr[mid1] === key) return mid1
+
+ // return index of key if found
+ if (arr[mid2] === key) 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 {
- // if low > high => we have searched the whole array without finding the item
- return -1
+ // the key lies in between mid1 and mid2
+ return ternarySearchRecursive(arr, key, mid1 + 1, mid2 - 1)
}
}
@@ -54,14 +49,11 @@ function ternarySearchIterative(arr, key, low = 0, high = arr.length - 1) {
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
- }
+ // return index of key if found
+ if (arr[mid1] === key) return mid1
+
+ // return index of key if found
+ if (arr[mid2] === key) return mid2
// since the key is not found at mid,
// check in which region it is present
@@ -75,8 +67,7 @@ function ternarySearchIterative(arr, key, low = 0, high = arr.length - 1) {
low = mid2 + 1
} else {
// the key lies in between mid1 and mid2
- low = mid1 + 1
- high = mid2 - 1
+ ;[low, high] = [mid1 + 1, mid2 - 1]
}
}
// the key was not found
diff --git a/Search/test/SentinelSearch.test.js b/Search/test/SentinelSearch.test.js
new file mode 100644
index 0000000000..dde901fa30
--- /dev/null
+++ b/Search/test/SentinelSearch.test.js
@@ -0,0 +1,13 @@
+import { sentinelSearch } from '../SentinelSearch'
+
+describe('Sentinel search', () => {
+ test.each([
+ [['o', 'b', 'c'], 'c', 2],
+ [[1, 2, 3, 4, 5], 4, 3],
+ [['s', 't', 'r', 'i', 'n', 'g'], 'a', null],
+ [['1', '2', '3'], '1', 0],
+ [['4', 'e', '6', '10'], 4, null]
+ ])('of %o , searching for %o, expected %i', (array, target, index) => {
+ expect(sentinelSearch(array, target)).toStrictEqual(index)
+ })
+})
diff --git a/Search/test/TernarySearch.test.js b/Search/test/TernarySearch.test.js
index 375c5c5fbd..a1a7a2ccd1 100644
--- a/Search/test/TernarySearch.test.js
+++ b/Search/test/TernarySearch.test.js
@@ -29,13 +29,13 @@ test('should return the index of a number in an array of numbers:', () => {
test('should return the index of a string in an array of strings:', () => {
const indexNumber = ternarySearchRecursive(
['Ali', 'Cathrynli', 'Josuke', 'Thomas'],
- 'Cathrynli'
+ 'Josuke'
)
- expect(indexNumber).toBe(1)
+ expect(indexNumber).toBe(2)
})
test('should return the index of a string in an array of strings:', () => {
- const indexNumber = ternarySearchRecursive(
+ const indexNumber = ternarySearchIterative(
['Ali', 'Cathrynli', 'Josuke', 'Thomas'],
'Josuke'
)
@@ -49,3 +49,11 @@ test('should return the index of a string in an array of strings:', () => {
)
expect(indexNumber).toBe(-1)
})
+
+test('should return the index of a string in an array of strings:', () => {
+ const indexNumber = ternarySearchIterative(
+ ['Ali', 'Cathrynli', 'Josuke', 'Thomas'],
+ 'Angela'
+ )
+ expect(indexNumber).toBe(-1)
+})