# Longest subsequence with at least one character appearing in every string

• Last Updated : 10 May, 2021

Given a string array arr[], the task is to find the longest sub-sequence of the array with at least one character appearing in all the strings. Note that all the strings contain only lowercase English alphabets.
Examples:

Input: str = {“ab”, “bc”, “de”}
Output:
{“ab”, “bc”} is the required sub-sequence
with ‘b’ as the common character.
Input: str = {“a”, “b”, “c”}
Output:

Approach: Create a count[] array such that count will store the number of strings which contain ‘a’, count will store the number of strings which contain ‘b’ and so on…
Now, it’s clear that the answer will be the maximum value from the count[] array. In order to update this array start traversing the string array and for every string, mark which characters are present in the current string in a hash[] array.
And after the traversal, for every character which is present in the current string update its count in the count[] array.
Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach``#include ``using` `namespace` `std;` `#define MAX 26` `// Function to return the length of the longest``// sub-sequence with at least one``// common character in every string``int` `largestSubSeq(string arr[], ``int` `n)``{` `    ``// count will store the number of strings``    ``// which contain 'a', count will store the``    ``// number of strings which contain 'b' and so on..``    ``int` `count[MAX] = { 0 };` `    ``// For every string``    ``for` `(``int` `i = 0; i < n; i++) {``        ``string str = arr[i];` `        ``// Hash array to set which character is``        ``// present in the current string``        ``bool` `hash[MAX] = { 0 };``        ``for` `(``int` `j = 0; j < str.length(); j++) {``            ``hash[str[j] - ``'a'``] = ``true``;``        ``}` `        ``for` `(``int` `j = 0; j < MAX; j++) {` `            ``// If current character appears in the``            ``// string then update its count``            ``if` `(hash[j])``                ``count[j]++;``        ``}``    ``}` `    ``return` `*(max_element(count, count + MAX));``}` `// Driver code``int` `main()``{``    ``string arr[] = { ``"ab"``, ``"bc"``, ``"de"` `};``    ``int` `n = ``sizeof``(arr) / ``sizeof``(string);` `    ``cout << largestSubSeq(arr, n);` `    ``return` `0;``}`

## Java

 `// Java implementation of the approach` `class` `GFG``{``        ` `    ``static` `int` `MAX = ``26``;``    ` `    ``// Function to return the length of the longest``    ``// sub-sequence with at least one``    ``// common character in every string``    ``static` `int` `largestSubSeq(String arr[], ``int` `n)``    ``{``    ` `        ``// count will store the number of strings``        ``// which contain 'a', count will store the``        ``// number of strings which contain 'b' and so on..``        ``int` `[] count = ``new` `int``[MAX];``    ` `        ``// For every string``        ``for` `(``int` `i = ``0``; i < n; i++) {``            ``String str = arr[i];``    ` `            ``// Hash array to set which character is``            ``// present in the current string``            ``boolean` `[] hash = ``new` `boolean``[MAX];``            ` `            ` `            ``for` `(``int` `j = ``0``; j < str.length(); j++) {``                ``hash[str.charAt(j) - ``'a'``] = ``true``;``            ``}``    ` `            ``for` `(``int` `j = ``0``; j < MAX; j++) {``    ` `                ``// If current character appears in the``                ``// string then update its count``                ``if` `(hash[j])``                    ``count[j]++;``            ``}``        ``}``        ` `        ``int` `max = -``1``;``    ` `        ``for``(``int` `i=``0``;i< MAX; i++)``        ``{``            ``if``(max < count[i])``                ``max = count[i];``        ``}``        ``return` `max;``    ``}``    ` `    ``// Driver code``    ``public` `static` `void` `main (String[] args)``    ``{``        ` `        ``String arr[] = { ``"ab"``, ``"bc"``, ``"de"` `};``        ``int` `n = arr.length;``    ` `        ``System.out.println(largestSubSeq(arr, n));``    `  `    ``}`  `}` `// This code is contributed by ihritik`

## Python3

 `# Python3 implementation of the approach``MAX` `=` `26` `# Function to return the length of the longest``# sub-sequence with at least one``# common character in every string``def` `largestSubSeq(arr, n):``    ` `    ``# count will store the number of strings``    ``# which contain 'a', count will store the``    ``# number of strings which contain 'b' and so on..``    ``count ``=` `[``0``] ``*` `MAX``    ` `    ``# For every string``    ``for` `i ``in` `range``(n):``        ``string ``=` `arr[i]``        ` `        ``# Hash array to set which character is``        ``# present in the current string``        ``_hash ``=` `[``False``] ``*` `MAX``        ``for` `j ``in` `range``(``len``(string)):``            ``_hash[``ord``(string[j]) ``-` `ord``(``'a'``)] ``=` `True``        ` `        ``for` `j ``in` `range``(``MAX``):``            ` `            ``# If current character appears in the``            ``# string then update its count``            ``if` `_hash[j] ``=``=` `True``:``                ``count[j] ``+``=` `1``                ` `    ``return` `max``(count)` `# Driver code``if` `__name__ ``=``=` `"__main__"``:``    ``arr ``=` `[ ``"ab"``, ``"bc"``, ``"de"` `]``    ``n ``=` `len``(arr)``    ``print``(largestSubSeq(arr, n))` `# This code is contributed by``# sanjeev2552`

## C#

 `// C# implementation of the approach``using` `System;` `class` `GFG``{``        ` `    ``static` `int` `MAX = 26;``    ` `    ``// Function to return the length of the longest``    ``// sub-sequence with at least one``    ``// common character in every string``    ``static` `int` `largestSubSeq(``string` `[] arr, ``int` `n)``    ``{``    ` `        ``// count will store the number of strings``        ``// which contain 'a', count will store the``        ``// number of strings which contain 'b' and so on..``        ``int` `[] count = ``new` `int``[MAX];``    ` `        ``// For every string``        ``for` `(``int` `i = 0; i < n; i++)``        ``{``            ``string` `str = arr[i];``    ` `            ``// Hash array to set which character is``            ``// present in the current string``            ``bool` `[] hash = ``new` `bool``[MAX];``            ` `            ` `            ``for` `(``int` `j = 0; j < str.Length; j++)``            ``{``                ``hash[str[j] - ``'a'``] = ``true``;``            ``}``    ` `            ``for` `(``int` `j = 0; j < MAX; j++)``            ``{``    ` `                ``// If current character appears in the``                ``// string then update its count``                ``if` `(hash[j])``                    ``count[j]++;``            ``}``        ``}``        ` `        ``int` `max = -1;``    ` `        ``for``(``int` `i=0;i< MAX; i++)``        ``{``            ``if``(max < count[i])``                ``max = count[i];``        ``}``        ``return` `max;``    ``}``    ` `    ``// Driver code``    ``public` `static` `void` `Main ()``    ``{``        ` `        ``string` `[] arr = { ``"ab"``, ``"bc"``, ``"de"` `};``        ``int` `n = arr.Length;``    ` `        ``Console.WriteLine(largestSubSeq(arr, n));``    ``}``}` `// This code is contributed by ihritik`

## Javascript

 ``

Output:

`2`

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