Minimum delete operations to make all elements of array same
Last Updated :
23 Jul, 2025
Given an array of n elements such that elements may repeat. We can delete any number of elements from the array. The task is to find a minimum number of elements to be deleted from the array to make it equal.
Examples:
Input: arr[] = {4, 3, 4, 4, 2, 4}
Output: 2
After deleting 2 and 3 from array, array becomes
arr[] = {4, 4, 4, 4}
Input: arr[] = {1, 2, 3, 4, 5}
Output: 4
We can delete any four elements from array.
In this problem, we need to minimize the delete operations. The approach is simple, we count the frequency of each element in an array, then find the frequency of the most frequent elements in count array. Let this frequency be max_freq. To get the minimum number of elements to be deleted from the array calculate n - max_freq where n is a number of elements in the given array.
C++
// C++ program to find minimum
// number of deletes required
// to make all elements same.
#include <bits/stdc++.h>
using namespace std;
// Function to get minimum number of elements to be deleted
// from array to make array elements equal
int minDelete(int arr[], int n)
{
// Create an hash map and store frequencies of all
// array elements in it using element as key and
// frequency as value
unordered_map<int, int> freq;
for (int i = 0; i < n; i++)
freq[arr[i]]++;
// Find maximum frequency among all frequencies.
int max_freq = INT_MIN;
for (auto itr = freq.begin(); itr != freq.end(); itr++)
max_freq = max(max_freq, itr->second);
// To minimize delete operations, we remove all
// elements but the most frequent element.
return n - max_freq;
}
// Driver program to run the case
int main()
{
int arr[] = { 4, 3, 4, 4, 2, 4 };
int n = sizeof(arr) / sizeof(arr[0]);
cout << minDelete(arr, n);
return 0;
}
// Java program to find minimum number
// of deletes required to make all
// elements same.
import java.util.*;
class GFG{
// Function to get minimum number of
// elements to be deleted from array
// to make array elements equal
static int minDelete(int arr[], int n)
{
// Create an hash map and store
// frequencies of all array elements
// in it using element as key and
// frequency as value
HashMap<Integer, Integer> freq = new HashMap<>();
for(int i = 0; i < n; i++)
freq.put(arr[i], freq.getOrDefault(arr[i], 0) + 1);
// Find maximum frequency among all frequencies.
int max_freq = Integer.MIN_VALUE;
for(Map.Entry<Integer,
Integer> entry : freq.entrySet())
max_freq = Math.max(max_freq,
entry.getValue());
// To minimize delete operations,
// we remove all elements but the
// most frequent element.
return n - max_freq ;
}
// Driver code
public static void main(String[] args)
{
int arr[] = { 4, 3, 4, 4, 2, 4 };
int n = arr.length;
System.out.print(minDelete(arr, n));
}
}
// This code is contributed by amal kumar choubey and corrected by Leela Kotte
# Python3 program to find minimum
# number of deletes required to
# make all elements same.
# Function to get minimum number
# of elements to be deleted from
# array to make array elements equal
def minDelete(arr, n):
# Create an dictionary and store
# frequencies of all array
# elements in it using
# element as key and
# frequency as value
freq = {}
for i in range(n):
if arr[i] in freq:
freq[arr[i]] += 1
else:
freq[arr[i]] = 1;
# Find maximum frequency
# among all frequencies.
max_freq = 0;
for i, j in freq.items():
max_freq = max(max_freq, j);
# To minimize delete operations,
# we remove all elements but the
# most frequent element.
return n - max_freq;
# Driver code
arr = [ 4, 3, 4, 4, 2, 4 ];
n = len(arr)
print(minDelete(arr, n));
# This code is contributed by grand_master
// C# program to find minimum number
// of deletes required to make all
// elements same.
using System;
using System.Collections.Generic;
class GFG {
// Function to get minimum number of
// elements to be deleted from array
// to make array elements equal
static int minDelete(int[] arr, int n)
{
// Create an hash map and store
// frequencies of all array elements
// in it using element as key and
// frequency as value
Dictionary<int, int> freq
= new Dictionary<int, int>();
for (int i = 0; i < n; i++)
if (freq.ContainsKey(arr[i]))
{
freq[arr[i]] = freq[arr[i]] + 1;
}
else
{
freq.Add(arr[i], 1);
}
// Find maximum frequency among all frequencies.
int max_freq = int.MinValue;
foreach(KeyValuePair<int, int> entry in freq)
max_freq = Math.Max(max_freq, entry.Value);
// To minimize delete operations,
// we remove all elements but the
// most frequent element.
return n - max_freq + 1;
}
// Driver code
public static void Main(String[] args)
{
int[] arr = {4, 3, 4, 4, 2, 4};
int n = arr.Length;
Console.Write(minDelete(arr, n));
}
}
// This code is contributed by Amit Katiyar
<script>
// Javascript program to find minimum number
// of deletes required to make all
// elements same.
// Function to get minimum number of
// elements to be deleted from array
// to make array elements equal
function minDelete(arr, n)
{
// Create an hash map and store
// frequencies of all array elements
// in it using element as key and
// frequency as value
let freq = new Map();
for(let i = 0; i < n; i++){
if(freq.has(arr[i])){
freq.set(arr[i], freq.get(arr[i]) + 1)
}else{
freq.set(arr[i], 1)
}
}
// Find maximum frequency among all frequencies.
let max_freq = Number.MIN_SAFE_INTEGER;
for(let entry of freq)
max_freq = Math.max(max_freq, entry[1]);
// To minimize delete operations,
// we remove all elements but the
// most frequent element.
return n - max_freq ;
}
// Driver code
let arr = [4, 3, 4, 4, 2, 4 ];
let n = arr.length;
document.write(minDelete(arr, n));
// This code is contributed by _saurabh_jaiswal.
</script>
Output:
2
Time complexity: O(n)
Auxiliary Space: O(n)
Another Approach Using binary search :
- .First , we will sort the array for binary search function . Then we can find frequency of all array elements using lower_bound and upper bound .
- Then our answer will be n - max_frequency .
- Then return final answer
Below is the implementation of the above approach:
C++
// C++ implementation of the above approach
#include <bits/stdc++.h>
using namespace std;
// Function to find minimum operation required to
// make all array elements equal
int minDelete(int arr[], int n)
{
int max_freq = 1;
sort(arr,arr+n);//sort array for binary search
// Iterating the whole array
for(int i = 0 ; i < n ;i++)
{
//index of first and last occ of arr[i]
int first_index = lower_bound(arr,arr+n,arr[i])- arr;
int last_index = upper_bound(arr,arr+n,arr[i])- arr-1;
i = last_index; // assign i to last_index to avoid
// same element multiple time
int fre = last_index-first_index+1;//finding frequency
// Finding maximum frequency from all array elements
max_freq = max( max_freq , fre );
}
return n-max_freq;// return answer
}
// Drive code
int main()
{
int arr[] = { 4, 3, 4, 4, 2, 4 };
int n = sizeof(arr) / sizeof(arr[0]);
// Function call
cout << minDelete(arr, n);
return 0;
}
// This Approach is contributed by nikhilsainiofficial546
import java.util.Arrays;
public class Main {
// Function to find minimum operation required to make all
// array elements equal
public static int minDelete(int[] arr) {
int n = arr.length;
int max_freq = 1;
Arrays.sort(arr); // sort array for binary search
// Iterating the whole array
for (int i = 0; i < n; i++) {
// index of first and last occurrence of arr[i]
int first_index = Arrays.binarySearch(arr, arr[i]);
int last_index = first_index;
while (last_index < n - 1 && arr[last_index + 1] == arr[i]) {
last_index++;
}
i = last_index; // assign i to last_index to avoid same element multiple times
int fre = last_index - first_index + 1; // finding frequency
// Finding maximum frequency from all array elements
max_freq = Math.max(max_freq, fre);
}
return n - max_freq; // return answer
}
public static void main(String[] args) {
int[] arr = {4, 3, 4, 4, 2, 4};
System.out.println(minDelete(arr));
}
}
# Function to find minimum operation required to
# make all array elements equal
def minDelete(arr, n):
max_freq = 1
arr.sort() # sort array for binary search
# Iterating the whole array
i = 0
while i < n:
# index of first occ of arr[i]
first_index = arr.index(arr[i])
# find the last occ of arr[i]
j = n - 1
while j >= 0 and arr[j] != arr[i]:
j -= 1
last_index = j
fre = last_index - first_index + 1 # finding frequency
# Finding maximum frequency from all array elements
max_freq = max(max_freq, fre)
i = last_index + 1 # assign i to next index
return n - max_freq # return answer
# Drive code
arr = [4, 3, 4, 4, 2, 4]
n = len(arr)
# Function call
print(minDelete(arr, n))
using System;
class Program {
// Function to find minimum operation required to
// make all array elements equal
static int minDelete(int[] arr, int n)
{
int max_freq = 1;
Array.Sort(arr); // sort array for binary search
// Iterating the whole array
for (int i = 0; i < n; i++) {
// index of first and last occ of arr[i]
int first_index
= Array.BinarySearch(arr, arr[i]);
int last_index = Array.LastIndexOf(arr, arr[i]);
i = last_index; // assign i to last_index to
// avoid same element multiple
// time
int fre = last_index - first_index
+ 1; // finding frequency
// Finding maximum frequency from all array
// elements
max_freq = Math.Max(max_freq, fre);
}
return n - max_freq; // return answer
}
static void Main(string[] args)
{
int[] arr = { 4, 3, 4, 4, 2, 4 };
int n = arr.Length;
// Function call
Console.WriteLine(minDelete(arr, n));
}
}
// This code is contributed by sarojmcy2e
// Function to find minimum operation required to
// make all array elements equal
function minDelete(arr, n) {
let max_freq = 1;
arr.sort((a, b) => a - b); // sort array for binary search
// Iterating the whole array
for (let i = 0; i < n; i++) {
// index of first and last occ of arr[i]
let first_index = arr.indexOf(arr[i]);
let last_index = arr.lastIndexOf(arr[i]);
i = last_index; // assign i to last_index to avoid
// same element multiple time
let fre = last_index - first_index + 1; // finding frequency
// Finding maximum frequency from all array elements
max_freq = Math.max(max_freq, fre);
}
return n - max_freq; // return answer
}
// Drive code
let arr = [4, 3, 4, 4, 2, 4];
let n = arr.length;
// Function call
console.log(minDelete(arr, n));
Time Complexity: O(N*Log2N), where N is the size of the input array
Auxiliary Space: O(1)
Note: Here we can optimize the extra space to count the frequency of each element to O(1) but for this, we have to modify our original array. See this article.
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