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# Find the frequency of each element in a sorted array

• Difficulty Level : Basic
• Last Updated : 22 Jul, 2021

Given a sorted array, arr[] consisting of N integers, the task is to find the frequencies of each array element.

Examples:

Input: arr[] = {1, 1, 1, 2, 3, 3, 5, 5, 8, 8, 8, 9, 9, 10}
Output: Frequency of 1 is: 3
Frequency of 2 is: 1
Frequency of 3 is: 2
Frequency of 5 is: 2
Frequency of 8 is: 3
Frequency of 9 is: 2
Frequency of 10 is: 1

Input: arr[] = {2, 2, 6, 6, 7, 7, 7, 11}
Output:  Frequency of 2 is: 2
Frequency of 6 is: 2
Frequency of 7 is: 3
Frequency of 11 is: 1

Naive Approach: The simplest approach is to traverse the array and keep the count of every element encountered in a HashMap and then, in the end, print the frequencies of every element by traversing the HashMap. This approach is already implemented here.

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

Efficient Approach: The above approach can be optimized in terms of space used based on the fact that, in a sorted array, the same elements occur consecutively, so the idea is to maintain a variable to keep track of the frequency of elements while traversing the array. Follow the steps below to solve the problem:

• Initialize a variable, say freq as 1 to store the frequency of elements.
• Iterate in the range [1, N-1] using the variable i and perform the following steps:
• If the value of arr[i] is equal to arr[i-1], increment freq by 1.
• Else print value the frequency of arr[i-1] obtained in freq and then update freq to 1.
• Finally, after the above step, print the frequency of the last distinct element of the array as freq.

Below is the implementation of the above approach:

## C++

 `// C++ program for the above approach``#include ``using` `namespace` `std;` `    ``// Function to print the frequency``    ``// of each element of the sorted array``     ``void` `printFreq(vector<``int``> &arr, ``int` `N)``    ``{``       ` `        ``// Stores the frequency of an element``        ``int` `freq = 1;``       ` `       ``// Traverse the array arr[]``        ``for` `(``int` `i = 1; i < N; i++)``        ``{``          ` `            ``// If the current element is equal``            ``// to the previous element``            ``if` `(arr[i] == arr[i - 1])``            ``{``              ` `                ``// Increment the freq by 1``                ``freq++;``            ``}``          ` `        ``// Otherwise,``            ``else` `{``                ``cout<<``"Frequency of "``< arr``            ``= { 1, 1, 1, 2, 3, 3, 5, 5,``                ``8, 8, 8, 9, 9, 10 };``        ``int` `N = arr.size();``      ` `        ``// Function Call``        ``printFreq(arr, N);``    ``return` `0;``    ``}   ` `// This code is contributed by codersaty`

## Java

 `// Java program for the above approach``import` `java.io.*;``import` `java.lang.*;``import` `java.util.*;` `class` `GFG {` `    ``// Function to print the frequency``    ``// of each element of the sorted array``    ``static` `void` `printFreq(``int` `arr[], ``int` `N)``    ``{` `        ``// Stores the frequency of an element``        ``int` `freq = ``1``;` `        ``// Traverse the array arr[]``        ``for` `(``int` `i = ``1``; i < N; i++) {``            ``// If the current element is equal``            ``// to the previous element``            ``if` `(arr[i] == arr[i - ``1``]) {``                ``// Increment the freq by 1``                ``freq++;``            ``}` `            ``// Otherwise,``            ``else` `{``                ``System.out.println(``"Frequency of "``                                   ``+ arr[i - ``1``]``                                   ``+ ``" is: "` `+ freq);``                ``// Update freq``                ``freq = ``1``;``            ``}``        ``}` `        ``// Print the frequency of the last element``        ``System.out.println(``"Frequency of "``                           ``+ arr[N - ``1``]``                           ``+ ``" is: "` `+ freq);``    ``}` `    ``// Driver Code``    ``public` `static` `void` `main(String args[])``    ``{``        ``// Given Input``        ``int` `arr[]``            ``= { ``1``, ``1``, ``1``, ``2``, ``3``, ``3``, ``5``, ``5``,``                ``8``, ``8``, ``8``, ``9``, ``9``, ``10` `};``        ``int` `N = arr.length;` `        ``// Function Call``        ``printFreq(arr, N);``    ``}``}`

## Python3

 `# Python3 program for the above approach` `# Function to print the frequency``# of each element of the sorted array``def` `printFreq(arr, N):``  ` `    ``# Stores the frequency of an element``    ``freq ``=` `1` `    ``# Traverse the array arr[]``    ``for` `i ``in` `range``(``1``, N, ``1``):``      ` `        ``# If the current element is equal``        ``# to the previous element``        ``if` `(arr[i] ``=``=` `arr[i ``-` `1``]):``          ` `            ``# Increment the freq by 1``            ``freq ``+``=` `1` `        ``# Otherwise,``        ``else``:``            ``print``(``"Frequency of"``,arr[i ``-` `1``],``"is:"``,freq)``                ``# Update freq``            ``freq ``=` `1` `    ``# Print the frequency of the last element``    ``print``(``"Frequency of"``,arr[N ``-` `1``],``"is:"``,freq)` `# Driver Code``if` `__name__ ``=``=` `'__main__'``:``  ` `    ``# Given Input``    ``arr ``=` `[``1``, ``1``, ``1``, ``2``, ``3``, ``3``, ``5``, ``5``,``8``, ``8``, ``8``, ``9``, ``9``, ``10``]``    ``N ``=` `len``(arr)` `    ``# Function Call``    ``printFreq(arr, N)``    ` `    ``# This code is contributed by ipg2016107.`

## C#

 `// C# program for the above approach``using` `System;` `public` `class` `GFG{``    ` `// Function to print the frequency``// of each element of the sorted array``static` `void` `printFreq(``int``[] arr, ``int` `N)``{` `    ``// Stores the frequency of an element``    ``int` `freq = 1;` `    ``// Traverse the array arr[]``    ``for` `(``int` `i = 1; i < N; i++)``    ``{` `      ``// If the current element is equal``      ``// to the previous element``      ``if` `(arr[i] == arr[i - 1])``      ``{` `        ``// Increment the freq by 1``        ``freq++;``      ``}` `      ``// Otherwise,``      ``else` `{``        ``Console.WriteLine(``"Frequency of "` `+ arr[i - 1] + ``" is: "` `+ freq);``        ``// Update freq``        ``freq = 1;``      ``}``    ``}` `    ``// Print the frequency of the last element``    ``Console.WriteLine(``"Frequency of "` `+ arr[N - 1] + ``" is: "` `+ freq);``}` `// Driver Code``static` `public` `void` `Main (){` `    ``// Given Input``    ``int``[] arr = { 1, 1, 1, 2, 3, 3, 5, 5,``                  ``8, 8, 8, 9, 9, 10 };``    ``int` `N = arr.Length;``      ` `    ``// Function Call``    ``printFreq(arr, N);``}``}` `// This code is contributed by Dharanendra L V.`

## Javascript

 ``
Output
```Frequency of 1 is: 3
Frequency of 2 is: 1
Frequency of 3 is: 2
Frequency of 5 is: 2
Frequency of 8 is: 3
Frequency of 9 is: 2
Frequency of 10 is: 1```

Time Complexity: O(N)
Auxiliary Space: O(1)

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