Moore's Voting Algorithm - Boyer-Moore Majority Voting Algorithm

DIRECTORY.md

@@ -73,6 +73,7 @@
     * [NumberOfLocalMaximumPoints](Data-Structures/Array/NumberOfLocalMaximumPoints.js)
     * [QuickSelect](Data-Structures/Array/QuickSelect.js)
     * [Reverse](Data-Structures/Array/Reverse.js)
+    * [MooreVotingAlgorithm](Data-Structures/Array/MooreVotingAlgorithm.js)
   * **Graph**
     * [Graph](Data-Structures/Graph/Graph.js)
     * [Graph2](Data-Structures/Graph/Graph2.js)

Data-Structures/Array/MooreVotingAlgorithm.js

@@ -0,0 +1,29 @@
+/**
+ * Moore Voting Algorithm to find the majority element in an array
+ * Majority element is the one that appears more than n/2 times
+ * geeksforgeeks: https://www.geeksforgeeks.org/boyer-moore-majority-voting-algorithm/
+ * @param {Array} arr array of integers
+ * @returns {Number} majority element or null if no majority exists
+ */
+const MooreVotingAlgorithm = (arr) => {
+  let candidate = null
+  let count = 0
+
+  // Phase 1: Find the candidate for majority element
+  for (let num of arr) {
+    if (count === 0) {
+      candidate = num
+    }
+    count += num === candidate ? 1 : -1
+  }
+
+  // Phase 2: Verify if the candidate is actually the majority element
+  count = 0
+  for (let num of arr) {
+    if (num === candidate) {
+      count++
+    }
+  }
+  return count > arr.length / 2 ? candidate : null
+}
+export { MooreVotingAlgorithm }

Data-Structures/Array/test/MooreVotingAlgorithm.test.js

@@ -0,0 +1,11 @@
+import { MooreVotingAlgorithm } from '../MooreVotingAlgorithm'
+describe('Moore Voting Algorithm', () => {
+  it.each([
+    [[1, 1, 2, 1, 3, 1, 1], 1], // Majority element 1
+    [[2, 2, 2, 2, 5, 5, 5, 2], 2], // Majority element 2
+    [[3], 3], // Single element, it's the majority
+    [[1, 2, 3, 4, 5, 6, 7], null] // No majority element in the array
+  ])('returns %j when given %j', (array, expected) => {
+    expect(MooreVotingAlgorithm(array)).toEqual(expected)
+  })
+})

Maths/MobiusFunction.js

@@ -18,16 +18,19 @@
  * @param {Integer} number
  * @returns {Integer}
  */
-
 import { PrimeFactors } from './PrimeFactors.js'
+
 export const mobiusFunction = (number) => {
-  const primeFactorsArray = PrimeFactors(number)
   if (number <= 0) {
     throw new Error('Number must be greater than zero.')
   }
-  return primeFactorsArray.length !== new Set(primeFactorsArray).size
-    ? 0
-    : primeFactorsArray.length % 2 === 0
-    ? 1
-    : -1
+
+  const primeFactorsArray = PrimeFactors(number)
+  const uniquePrimeFactors = new Set(primeFactorsArray)
+
+  // If there are duplicate factors, it means number is not square-free.
+  if (primeFactorsArray.length !== uniquePrimeFactors.size) {
+    return 0
+  }
+  return uniquePrimeFactors.size % 2 === 0 ? 1 : -1
 }

package.json

@@ -13,11 +13,11 @@
   "author": "TheAlgorithms",
   "license": "GPL-3.0",
   "devDependencies": {
+    "@vitest/coverage-v8": "^1.2.1",
     "globby": "^13.2.2",
     "husky": "^8.0.3",
-    "prettier": "^3.0.3",
-    "vitest": "^1.2.1",
-    "@vitest/coverage-v8": "^1.2.1"
+    "prettier": "^3.3.3",
+    "vitest": "^1.2.1"
   },
   "engines": {
     "node": ">=20.6.0"