# Minimum deletions required such that any number X will occur exactly X times

Given an array **arr[]** of **N** integers, the task is to find the minimum deletions required such that frequency of **arr[i]** is exactly **arr[i]** in the array for all possible values of **i**.**Examples:**

Input:arr[] = {1, 2, 2, 3, 3}Output:2

Frequency(1) = 1

Frequency(2) = 2

Frequency(3) = 2, frequency can’t be increased

So, delete every occurrence of 3.Input:arr[] = {2, 3, 2, 3, 4, 4, 4, 4, 5}Output:3

**Approach:** There are two cases:

- If frequency of X is greater than or equal o X then we delete extra frequencies of X to get exactly X elements of value X.
- If frequency of X is less than X then we delete all of the occurrences of X as it is impossible to get extra element of value X.

Below is the implementation of the above approach:

## C++

`// C++ implementation of the approach` `#include <bits/stdc++.h>` `using` `namespace` `std;` `// Function to return the minimum` `// deletions required` `int` `MinDeletion(` `int` `a[], ` `int` `n)` `{` ` ` `// To store the frequency of` ` ` `// the array elements` ` ` `unordered_map<` `int` `, ` `int` `> map;` ` ` `// Store frequency of each element` ` ` `for` `(` `int` `i = 0; i < n; i++)` ` ` `map[a[i]]++;` ` ` `// To store the minimum deletions required` ` ` `int` `ans = 0;` ` ` `for` `(` `auto` `i : map) {` ` ` `// Value` ` ` `int` `x = i.first;` ` ` `// It's frequency` ` ` `int` `frequency = i.second;` ` ` `// If number less than or equal` ` ` `// to it's frequency` ` ` `if` `(x <= frequency) {` ` ` `// Delete extra occurrences` ` ` `ans += (frequency - x);` ` ` `}` ` ` `// Delete every occurrence of x` ` ` `else` ` ` `ans += frequency;` ` ` `}` ` ` `return` `ans;` `}` `// Driver code` `int` `main()` `{` ` ` `int` `a[] = { 2, 3, 2, 3, 4, 4, 4, 4, 5 };` ` ` `int` `n = ` `sizeof` `(a) / ` `sizeof` `(a[0]);` ` ` `cout << MinDeletion(a, n);` ` ` `return` `0;` `}` |

## Java

`// Java Implementation of above approach` `import` `java.util.*;` `class` `GFG` `{` ` ` `// Function to return the minimum` `// deletions required` `static` `int` `MinDeletion(` `int` `a[], ` `int` `n)` `{` ` ` `// To store the frequency of` ` ` `// the array elements` ` ` `Map<Integer,Integer> mp = ` `new` `HashMap<>();` ` ` `// Store frequency of each element` ` ` `for` `(` `int` `i = ` `0` `; i < n; i++)` ` ` `{` ` ` `if` `(mp.containsKey(a[i]))` ` ` `{` ` ` `mp.put(a[i], mp.get(a[i])+` `1` `);` ` ` `}` ` ` `else` ` ` `{` ` ` `mp.put(a[i], ` `1` `);` ` ` `}` ` ` `}` ` ` `// To store the minimum deletions required` ` ` `int` `ans = ` `0` `;` ` ` `for` `(Map.Entry<Integer,Integer> i : mp.entrySet())` ` ` `{` ` ` `// Value` ` ` `int` `x = i.getKey();` ` ` `// It's frequency` ` ` `int` `frequency = i.getValue();` ` ` `// If number less than or equal` ` ` `// to it's frequency` ` ` `if` `(x <= frequency)` ` ` `{` ` ` `// Delete extra occurrences` ` ` `ans += (frequency - x);` ` ` `}` ` ` `// Delete every occurrence of x` ` ` `else` ` ` `ans += frequency;` ` ` `}` ` ` `return` `ans;` `}` `// Driver code` `public` `static` `void` `main(String[] args)` `{` ` ` `int` `a[] = { ` `2` `, ` `3` `, ` `2` `, ` `3` `, ` `4` `, ` `4` `, ` `4` `, ` `4` `, ` `5` `};` ` ` `int` `n = a.length;` ` ` `System.out.println(MinDeletion(a, n));` `}` `}` `// This code is contributed by Rajput-Ji` |

## Python3

`# Python3 implementation of the approach` `# Function to return the minimum` `# deletions required` `def` `MinDeletion(a, n) :` ` ` `# To store the frequency of` ` ` `# the array elements` ` ` `map` `=` `dict` `.fromkeys(a, ` `0` `);` ` ` `# Store frequency of each element` ` ` `for` `i ` `in` `range` `(n) :` ` ` `map` `[a[i]] ` `+` `=` `1` `;` ` ` `# To store the minimum deletions required` ` ` `ans ` `=` `0` `;` ` ` `for` `key,value ` `in` `map` `.items() :` ` ` `# Value` ` ` `x ` `=` `key;` ` ` `# It's frequency` ` ` `frequency ` `=` `value;` ` ` `# If number less than or equal` ` ` `# to it's frequency` ` ` `if` `(x <` `=` `frequency) :` ` ` `# Delete extra occurrences` ` ` `ans ` `+` `=` `(frequency ` `-` `x);` ` ` `# Delete every occurrence of x` ` ` `else` `:` ` ` `ans ` `+` `=` `frequency;` ` ` `return` `ans;` `# Driver code` `if` `__name__ ` `=` `=` `"__main__"` `:` ` ` `a ` `=` `[ ` `2` `, ` `3` `, ` `2` `, ` `3` `, ` `4` `, ` `4` `, ` `4` `, ` `4` `, ` `5` `];` ` ` `n ` `=` `len` `(a);` ` ` `print` `(MinDeletion(a, n));` `# This code is contributed by AnkitRai01` |

## C#

`// C# Implementation of above approach` `using` `System;` `using` `System.Collections.Generic;` `class` `GFG` `{` ` ` `// Function to return the minimum` `// deletions required` `static` `int` `MinDeletion(` `int` `[]a, ` `int` `n)` `{` ` ` `// To store the frequency of` ` ` `// the array elements` ` ` `Dictionary<` `int` `,` ` ` `int` `> mp = ` `new` `Dictionary<` `int` `,` ` ` `int` `>();` ` ` `// Store frequency of each element` ` ` `for` `(` `int` `i = 0 ; i < n; i++)` ` ` `{` ` ` `if` `(mp.ContainsKey(a[i]))` ` ` `{` ` ` `var` `val = mp[a[i]];` ` ` `mp.Remove(a[i]);` ` ` `mp.Add(a[i], val + 1);` ` ` `}` ` ` `else` ` ` `{` ` ` `mp.Add(a[i], 1);` ` ` `}` ` ` `}` ` ` ` ` `// To store the minimum deletions required` ` ` `int` `ans = 0;` ` ` `foreach` `(KeyValuePair<` `int` `, ` `int` `> i ` `in` `mp)` ` ` `{` ` ` `// Value` ` ` `int` `x = i.Key;` ` ` `// It's frequency` ` ` `int` `frequency = i.Value;` ` ` `// If number less than or equal` ` ` `// to it's frequency` ` ` `if` `(x <= frequency)` ` ` `{` ` ` `// Delete extra occurrences` ` ` `ans += (frequency - x);` ` ` `}` ` ` `// Delete every occurrence of x` ` ` `else` ` ` `ans += frequency;` ` ` `}` ` ` `return` `ans;` `}` `// Driver code` `public` `static` `void` `Main(String[] args)` `{` ` ` `int` `[]a = { 2, 3, 2, 3, 4, 4, 4, 4, 5 };` ` ` `int` `n = a.Length;` ` ` `Console.WriteLine(MinDeletion(a, n));` `}` `}` `// This code is contributed by PrinciRaj1992` |

## Javascript

`<script>` `// javaScript implementation of the approach` `// Function to return the minimum` `// deletions required` `function` `MinDeletion( a, n){` ` ` `// To store the frequency of` ` ` `// the array elements` ` ` `let map = ` `new` `Map();` ` ` ` ` `// Store frequency of each element` ` ` `for` `(let i = 0; i < n; i++){` ` ` `if` `(map[a[i]])` ` ` `map[a[i]]++;` ` ` `else` ` ` `map[a[i]] = 1` ` ` `}` ` ` `// To store the minimum deletions required` ` ` `let ans = 0;` ` ` `for` `(` `var` `m ` `in` `map){` ` ` ` ` `// Value` ` ` `let x = m;` ` ` `// It's frequency` ` ` `let frequency = map[m];` ` ` `// If number less than or equal` ` ` `// to it's frequency` ` ` `if` `(x <= frequency) {` ` ` `// Delete extra occurrences` ` ` `ans += (frequency - x);` ` ` `}` ` ` `// Delete every occurrence of x` ` ` `else` ` ` `ans += frequency;` ` ` `};` ` ` `return` `ans;` `}` `// Driver code` `let a = [ 2, 3, 2, 3, 4, 4, 4, 4, 5 ];` `let n = a.length;` `document.write( MinDeletion(a, n));` `// This code is contributed by rohitsingh07052.` `</script>` |

**Output:**

3

**Time Complexity:** O(N)

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