# Find minimum changes required in an array for it to contain k distinct elements

Given an array arr of size N and a number K. The task is to find the minimum elements to be replaced in the array with any number such that the array consists of K distinct elements.

Note: The array might consist of repeating elements.
Examples:

Input : arr[]={1, 2, 2, 8}, k = 1
Output : 2
The elements to be changed are 1, 8

Input : arr[]={1, 2, 7, 8, 2, 3, 2, 3}, k = 2
Output : 3
The elements to be changed are 1, 7, 8

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach: Since the task is to replace minimum elements from the array so we won’t replace elements which have more frequency in the array. So just define an array freq[] which stores the frequency of each number present in the array arr, then sort freq in descending order. So, first k elements of freq array don’t need to be replaced.

Below is the implementation of the above approach :

 // CPP program to minimum changes required  // in an array for k distinct elements. #include using namespace std;    #define MAX 100005    // Function to minimum changes required  // in an array for k distinct elements. int Min_Replace(int arr[], int n, int k) {     sort(arr, arr + n);        // Store the frequency of each element     int freq[MAX];            memset(freq, 0, sizeof freq);            int p = 0;     freq[p] = 1;            // Store the frequency of elements     for (int i = 1; i < n; i++) {         if (arr[i] == arr[i - 1])             ++freq[p];         else             ++freq[++p];     }        // Sort frequencies in descending order     sort(freq, freq + n, greater());            // To store the required answer     int ans = 0;     for (int i = k; i <= p; i++)         ans += freq[i];                // Return the required answer     return ans; }    // Driver code int main() {     int arr[] = { 1, 2, 7, 8, 2, 3, 2, 3 };            int n = sizeof(arr) / sizeof(arr[0]);            int k = 2;            cout << Min_Replace(arr, n, k);            return 0; }

 // C# program to minimum changes required  // in an array for k distinct elements. import java.util.*;    class GFG {     static int MAX = 100005;            // Function to minimum changes required      // in an array for k distinct elements.     static int Min_Replace(int [] arr,                             int n, int k)     {         Arrays.sort(arr);                // Store the frequency of each element         Integer [] freq = new Integer[MAX];         Arrays.fill(freq, 0);         int p = 0;         freq[p] = 1;                    // Store the frequency of elements         for (int i = 1; i < n; i++)         {             if (arr[i] == arr[i - 1])                 ++freq[p];             else                 ++freq[++p];         }                // Sort frequencies in descending order         Arrays.sort(freq, Collections.reverseOrder());                    // To store the required answer         int ans = 0;         for (int i = k; i <= p; i++)             ans += freq[i];                        // Return the required answer         return ans;     }            // Driver code     public static void main (String []args)     {         int [] arr = { 1, 2, 7, 8, 2, 3, 2, 3 };                    int n = arr.length;                    int k = 2;                    System.out.println(Min_Replace(arr, n, k));     } }    // This code is contributed by PrinciRaj1992

 # Python 3 program to minimum changes required  # in an array for k distinct elements. MAX = 100005    # Function to minimum changes required  # in an array for k distinct elements. def Min_Replace(arr, n, k):     arr.sort(reverse = False)        # Store the frequency of each element     freq = [0 for i in range(MAX)]            p = 0     freq[p] = 1            # Store the frequency of elements     for i in range(1, n, 1):         if (arr[i] == arr[i - 1]):             freq[p] += 1         else:             p += 1             freq[p] += 1        # Sort frequencies in descending order     freq.sort(reverse = True)            # To store the required answer     ans = 0     for i in range(k, p + 1, 1):         ans += freq[i]                # Return the required answer     return ans    # Driver code if __name__ == '__main__':     arr = [1, 2, 7, 8, 2, 3, 2, 3]            n = len(arr)            k = 2            print(Min_Replace(arr, n, k))        # This code is contributed by # Surendra_Gangwar

 // C# program to minimum changes required  // in an array for k distinct elements. using System;    class GFG {     static int MAX = 100005;            // Function to minimum changes required      // in an array for k distinct elements.     static int Min_Replace(int [] arr,                             int n, int k)     {         Array.Sort(arr);                // Store the frequency of each element         int [] freq = new int[MAX];                    int p = 0;         freq[p] = 1;                    // Store the frequency of elements         for (int i = 1; i < n; i++)         {             if (arr[i] == arr[i - 1])                 ++freq[p];             else                 ++freq[++p];         }                // Sort frequencies in descending order         Array.Sort(freq);         Array.Reverse(freq);                    // To store the required answer         int ans = 0;         for (int i = k; i <= p; i++)             ans += freq[i];                        // Return the required answer         return ans;     }            // Driver code     public static void Main ()     {         int [] arr = { 1, 2, 7, 8, 2, 3, 2, 3 };                    int n = arr.Length;                    int k = 2;                    Console.WriteLine(Min_Replace(arr, n, k));     } }    // This code is contributed by ihritik

Output:

3

Time Complexity : O(NlogN)

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