C++ Program to Find the Frequency of Elements in an Array (original) (raw)

Last Updated : 20 Mar, 2024

In C++, arrays are a type of data structure that can store a fixed-size sequential collection of elements of the same type. In this article, we will learn how to find the frequency of elements in an array in C++.

**Example:

**Input: Array: {1, 2, 3, 4, 2, 1, 3, 2, 4, 5}

**Output: Element: 1, Frequency: 2 Element: 2, Frequency: 3 Element: 3, Frequency: 2 Element: 4, Frequency: 2 Element: 5, Frequency: 1

Frequency of Elements in an Array in C++

To find the frequency of all the elements in an array in C++, we can use the unordered_map with the array elements as the key and its frequency as its value. We can then traverse the array and increment the frequency of each element.

Approach

• Create an unordered_map to store the frequency of each element. The keys of the map will be the elements from the array, and the corresponding values will be their frequencies.
• Iterate through each element of the array.
• For each element encountered in the array, increment its frequency count in the hash map. If the element is encountered for the first time, initialize its frequency count to 1.
• After traversing the entire array, iterate through the hash map. For each key-value pair in the hash map, print the element and its corresponding frequency.

C++ Program to Find the Frequency of Elements in an Array

C++ `

// C++ Program to illustrate how to find the frequency of // elements in an array #include #include using namespace std;

// Driver Code int main() { // Declaring an array of integers int arr[] = { 10, 20, 20, 10, 30, 40, 10, 20 }; int n = sizeof(arr) / sizeof(arr[0]);

// Declaring an unordered_map to store the frequency of
// elements
unordered_map<int, int> frequencyMap;

// Counting the frequency of elements
for (int i = 0; i < n; i++) {
    frequencyMap[arr[i]]++;
}

// Printing the frequency of elements
cout << "Frequency of elements in the array is: "
     << endl;
for (auto& i : frequencyMap) {
    cout << i.first << " -> " << i.second << endl;
}

return 0;

}

`

Output

Frequency of elements in the array is: 40 -> 1 30 -> 1 20 -> 3 10 -> 3

**Time Complexity: O(N), where N is the number of array elements.
**Auxiliary Space: O(N)