JavaScript Program for Finding the Majority Element of an Array

Finding the majority element in an array is a common problem in computer science and data analysis. The majority element in an array is the element that appears more than n/2 times, where n is the length of the array. In other words, it’s the element that occurs more frequently than any other element in the array.

Examples:

Input: arr=[2, 2, 3, 4, 2, 2, 5]
Output: 2
Explanation: 2 appears more than n/2 times

Input: arr=[2, 3, 3, 3, 2, 2, 3]
Output: 3
Explanation: 3 appears more than n/2 times

Method 1: Brute Force Approach:

Count the occurrences of each element and check if any element appears more than n/2 times.

Syntax:

for (let i = 0; i < n; i++) {
    //implementation
    if (count > n / 2) {
        return arr[i];
    }
}

Example: Below is the implementation of the above approach

Javascript

function findMajority(arr)
{
    const n = arr.length;
    for (let i = 0; i < n; i++) {
        let count = 0;
        for (let j = 0; j < n; j++)
        {
            if (arr[i] === arr[j]) {
                count++;
            }
        }
        if (count > n / 2)
        {
            return arr[i];
        }
    }
    return null;
}
const arr1 = [2, 2, 3, 4, 2, 2, 5];
console.log(findMajority(arr1));

Output

2

Method 2: Sorting Approach:

Sort the array and the majority element will be the middle element (n/2-th element).

Syntax:

arr.sort((a, b) => a - b);
return arr[majorityIndex];

Example: Below is the implementation of the above approach

Javascript

function findMajority(arr) {
    arr.sort((a, b) => a - b);
    const majorityIndex =
        Math.floor(arr.length / 2);
    return arr[majorityIndex];
}
const arr2 =
    [2, 2, 3, 4, 2, 2, 5];
console.log(findMajority(arr2));

Output

2

Method 3: Boyer-Moore Voting Algorithm:

This algorithm finds the majority element in linear time and constant space

Syntax:

let candidate = null;
let count = 0;
for (let num of arr) {
    if (count === 0) {
        candidate = num;
    }
    count += (num === candidate) 
        ? 1 : -1;
}
return candidate;

Example: Below is the implementation of the above approach

Javascript

function findMajority(arr) {
    let candidate = null;
    let count = 0;
    for (let num of arr) {
        if (count === 0) {
            candidate = num;
        }
        count += (num === candidate)
            ? 1 : -1;
    }
    return candidate;
}
const arr3 = [2, 2, 3, 4, 2, 2, 5];
console.log(findMajority(arr3));

Output

2