Majority Element in an Array in C++

April 28, 2023

Majority Element in array in C++ Language

In this page we will look into a coding question where we will learn how to find the element which occurs majority number of times in array in C++ Programming Language. There might be different approach to solve this question, one you will find here. If your approach is bit different post it onto the comment section.

Majority Element In An Array In C++

The Boyer-Moore Majority Vote Algorithm is a widely used algorithm for finding the majority element in an array. The majority element in an array in C++ is an element that appears more than n/2 times, where n is the size of the array.

This Algorithm is efficient with a time complexity of O(n) and a space complexity of O(1), as it uses constant extra space to maintain the candidate and count variables. It is a clever algorithm that leverages the properties of majority elements to find them efficiently in linear time.

Reverse an array or string

Sorting of Array

Array Rotation

Largest Sum Contigous SubArray

Boyer-Moore’s Voting Algorithm

Algorithm

Initialize a variable candidate to store the candidate element, and set it to the first element of the array arr[0].
Initialize a variable count to store the count of occurrences of the candidate element, and set it to 1.
Iterate through the array arr from index 1 to n-1:
- If count is 0, set the current element as the new candidate element and increment count to 1.
- If the current element is equal to the candidate element, increment count by 1.
- If the current element is not equal to the candidate element, decrement count by 1.
Reset count to 0.
Iterate through the array arr again to verify if the candidate element is a majority element:
- If the current element is equal to the candidate element, increment count by 1.
If count is greater than n/2, return the candidate element as the majority element.
If no majority element is found, return -1.

Program for finding the element that occurs most time in an array

Run

#include <iostream>
using namespace std;

int findMajorityElement (int arr[], int n)
{
  int candidate = 0;		// Candidate for majority element
  int count = 0;		// Count of occurrences of candidate element

  // Candidate selection phase
  for (int i = 0; i < n; i++)
    {
      if (count == 0)
	{
	  candidate = arr[i];	// Set current element as candidate
	  count = 1;
	}
      else if (arr[i] == candidate)
	{
	  count++;	
	}
      else
	{
	  count--;		
	}
    }

  // Verification phase
  count = 0;
  for (int i = 0; i < n; i++)
    {
      if (arr[i] == candidate)
	{
	  count++;		// Count occurrences of candidate element
	}
    }


  if (count > n / 2)
    {
      return candidate;
    }
  else
    {
      return -1;		// No majority element found
    }
}

int main ()
{
  int arr[] = { 3, 3, 4, 2, 4, 4, 2, 4, 4 };	// Example array
  int n = sizeof (arr) / sizeof (arr[0]);
  int majorityElement = findMajorityElement (arr, n);

  if (majorityElement != -1)
    {
      cout << "Majority element is: " << majorityElement << endl;
    }
  else
    {
      cout << "No majority element found" << endl;
    }

  return 0;
}

Output

Majority Element = 4

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