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 stringint 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 codeint 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 approachMAX = 26 # Function to return the length of the longest# sub-sequence with at least one# common character in every stringdef 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 =  * 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 codeif __name__ == "__main__":    arr = [ "ab", "bc", "de" ]    n = len(arr)    print(largestSubSeq(arr, n)) # This code is contributed by# sanjeev2552

C#

 // C# implementation of the approachusing 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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