How to Find the Mode of Numbers in an Array in C++?

Mode of any dataset is the item that occurs most frequently in it. In this article, we will find the mode of numbers in an unsorted array in C++.

For Example,

Input:
myArray = { 1, 2, 3, 4, 5, 2, 3, 2, 2, 4, 2 }

Output:
Mode : 2

Finding Mode of Array Elements in C++

To find the mode of the array elements, we need to count the frequency of all elements in the array. To do that, we can use the std::unordered_map container where the key will represent the array element and its value will represent its frequency.

Approach

1. Create an unordered_map of <int, int>.
2. Start traversing the array.
3. Now, if the array element is present in the unordered_map, increment its value.
4. If the array element is not present, add the array element as key with value 1.
5. Finally, use std::max_element algorithm to find the maximum frequency and hence mode of the numbers.

C++ Program to Find Mode of Array Elements

C++

// C++ program to find the mode of an array
#include <algorithm>
#include <iostream>
#include <unordered_map>

using namespace std;

// Function to find the mode of an array
int findMode(int arr[], int n)
{
    // Create a frequency map to count occurrences of each
    // element
    unordered_map<int, int> freqMap;
    for (int i = 0; i < n; i++) {
        freqMap[arr[i]]++;
    }

    // Find the element with the maximum frequency
    auto maxElement
        = max_element(freqMap.begin(), freqMap.end(),
                      [](const auto& a, const auto& b) {
                          return a.second < b.second;
                      });

    // Return the mode (element with maximum frequency)
    return maxElement->first;
}

int main()
{
    // Test array
    int arr[] = { 2, 2, 3, 3, 3, 4 };
    int n = sizeof(arr) / sizeof(arr[0]);
    // Find and print the mode of the array
    cout << "Mode of the array is " << findMode(arr, n)
         << endl;
    return 0;
}

Output

Mode of the array is 3

Time Complexity: O(n)
Auxiliary Space: O(n)