# Find the length of the longest subsequence with first K alphabets having same frequency

Given a string str with uppercase characters and an integer K, the task is to find the length of the longest subsequence such that the frequency of first K alphabets is same.

Examples:

Input: str = “ACAABCCAB”, K=3
Output: 6
Explanation: One of the possible subsequences is “ACABCB”.

Input: str = “ACAABCCAB”, K=4
Output: 0
Explanation: Since, the string does not contain ‘D’, no such subsequence can be obtained.

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

Approach:
Traverse the string and find the least frequent of the first K alphabets. Once found, (frequency of that element) * K gives the desired result.

Below is the implementation of the above approach:

## C++

 `// C++ program to find the longest  ` `// subsequence with first K  ` `// alphabets having same frequency  ` ` `  `#include   ` `using` `namespace` `std;  ` ` `  `// Function to return the  ` `// length of the longest  ` `// subsequence with first K  ` `// alphabets having same frequency  ` `int` `lengthOfSubsequence(string str,  ` `                            ``int` `K)  ` `{  ` `    ``// Map to store frequency  ` `    ``// of all characters in  ` `    ``// the string  ` `    ``map<``char``,``int``> mp;  ` `    ``for` `(``char` `ch : str) {  ` `        ``mp[ch]++;  ` `    ``}  ` `     `  `    ``// Variable to store the  ` `    ``// frequency of the least  ` `    ``// frequent of first K  ` `    ``// alphabets  ` `    ``int` `minimum = mp[``'A'``];  ` `    ``for` `(``int` `i = 1; i < K; i++) {  ` `        ``minimum = min(minimum,  ` `                    ``mp[(``char``)(i + ``'A'``)]);  ` `    ``}  ` `     `  `    ``return` `minimum * K;  ` `}  ` ` `  `int` `main()  ` `{  ` `    ``string str = ``"ACAABCCAB"``;  ` `    ``int` `K = 3;  ` `     `  `    ``cout << lengthOfSubsequence(str, K);  ` `    ``return` `0;  ` `}  `

## Java

 `// Java program to find the longest  ` `// subsequence with first K alphabets  ` `// having same frequency  ` `import` `java.util.*;  ` ` `  `class` `GFG{  ` ` `  `// Function to return the  ` `// length of the longest  ` `// subsequence with first K  ` `// alphabets having same frequency  ` `static` `int` `lengthOfSubsequence(String str,  ` `                            ``int` `K)  ` `{  ` `     `  `    ``// Map to store frequency  ` `    ``// of all characters in  ` `    ``// the string  ` `    ``Map mp = ``new` `HashMap<>();  ` `    ``for``(``char` `ch : str.toCharArray())  ` `    ``{  ` `        ``mp.put(ch, mp.getOrDefault(ch, ``0``) + ``1``);  ` `    ``}  ` ` `  `    ``// Variable to store the  ` `    ``// frequency of the least  ` `    ``// frequent of first K  ` `    ``// alphabets  ` `    ``int` `minimum = mp.get(``'A'``);  ` `    ``for``(``int` `i = ``1``; i < K; i++)  ` `    ``{  ` `        ``minimum = Math.min(minimum,  ` `                        ``mp.get((``char``)(i + ``'A'``)));  ` `    ``}  ` `    ``return` `minimum * K;  ` `}  ` ` `  `// Driver code  ` `public` `static` `void` `main(String[] args)  ` `{  ` `    ``String str = ``"ACAABCCAB"``;  ` `    ``int` `K = ``3``;  ` `     `  `    ``System.out.println(lengthOfSubsequence(str, K));  ` `}  ` `}  ` ` `  `// This code is contributed by offbeat  `

## Python3

 `# Python3 program to find the longest  ` `# subsequence with first K alphabets  ` `# having same frequency  ` `from` `collections ``import` `defaultdict  ` ` `  `# Function to return the  ` `# length of the longest  ` `# subsequence with first K  ` `# alphabets having same frequency  ` `def` `lengthOfSubsequence(st, K):  ` ` `  `    ``# Map to store frequency  ` `    ``# of all characters in  ` `    ``# the string  ` `    ``mp ``=` `defaultdict(``int``)  ` `    ``for` `ch ``in` `st:  ` `        ``mp[ch] ``+``=` `1` `     `  `    ``# Variable to store the  ` `    ``# frequency of the least  ` `    ``# frequent of first K  ` `    ``# alphabets  ` `    ``minimum ``=` `mp[``'A'``]  ` `     `  `    ``for` `i ``in` `range``(``1``, K):  ` `        ``minimum ``=` `min``(minimum,  ` `                    ``mp[``chr``(i ``+` `ord``(``'A'``))])  ` `     `  `    ``return` `(minimum ``*` `K)  ` ` `  `# Driver code  ` `if` `__name__ ``=``=` `"__main__"``:  ` `     `  `    ``st ``=` `"ACAABCCAB"` `    ``K ``=` `3` `     `  `    ``print``(lengthOfSubsequence(st, K))  ` ` `  `# This code is contributed by chitranayal  `

## C#

 `// C# program to find the longest ` `// subsequence with first K alphabets ` `// having same frequency ` `using` `System; ` `using` `System.Collections.Generic; ` ` `  `class` `GFG{ ` ` `  `// Function to return the ` `// length of the longest ` `// subsequence with first K ` `// alphabets having same frequency ` `static` `int` `lengthOfSubsequence(``string` `str, ` `                               ``int` `K) ` `{ ` `     `  `    ``// Store frequency ` `    ``// of all characters in ` `    ``// the string ` `    ``Dictionary<``char``, ` `               ``int``> mp = ``new` `Dictionary<``char``, ` `                                        ``int``>(); ` `     `  `    ``foreach``(``char` `ch ``in` `str.ToCharArray()) ` `    ``{ ` `        ``mp[ch] = mp.GetValueOrDefault(ch, 0) + 1; ` `    ``} ` ` `  `    ``// Variable to store the frequency ` `    ``// of the least frequent of first K ` `    ``// alphabets ` `    ``int` `minimum = mp[``'A'``]; ` `    ``for``(``int` `i = 1; i < K; i++)  ` `    ``{ ` `        ``minimum = Math.Min(minimum,  ` `                           ``mp[(``char``)(i + ``'A'``)]); ` `    ``} ` `    ``return` `minimum * K; ` `} ` ` `  `// Driver code ` `public` `static` `void` `Main(``string``[] args) ` `{ ` `    ``string` `str = ``"ACAABCCAB"``; ` `    ``int` `K = 3; ` `     `  `    ``Console.Write(lengthOfSubsequence(str, K)); ` `} ` `} ` ` `  `// This code is contributed by rutvik_56 `

Output:

```6
``` My Personal Notes arrow_drop_up Check out this Author's contributed articles.

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Improved By : chitranayal, offbeat, rutvik_56