Longest common anagram subsequence from N strings

Difficulty Level : Medium
Last Updated : 09 Jul, 2021

Given N strings. Find the longest possible subsequence from each of these N strings such that they are anagram to each other. The task is to print the lexicographically largest subsequence among all the subsequences.

Examples:

Input: s[] = { geeks, esrka, efrsk }
Output: ske
First string has “eks”, Second string has “esk”, third string has “esk”. These three are anagrams. “ske” is lexoigrapically large.
Input: string s[] = { loop, lol, olive }
Output: ol

Approach :

Make a 2-D array of n*26 to store the frequency of each character in string.
After making frequency array, traverse in reverse direction for each digit and find the string which has the minimum characters of this type.
After complete reverse traversal, print the character that occurs the minimum number of times since it gives the lexicographically largest string.

Below is the implementation of the above approach.

C++

// C++ program to find longest possible
// subsequence anagram of N strings.
#include <bits/stdc++.h>
using namespace std;
const int MAX_CHAR = 26;
 
// function to store frequency of
// each character in each string
void frequency(int fre[][MAX_CHAR], string s[], int n)
{
    for (int i = 0; i < n; i++) {
        string str = s[i];
        for (int j = 0; j < str.size(); j++)
            fre[i][str[j] - 'a']++;       
    }
}
 
// function to Find longest possible sequence of N
// strings which is anagram to each other
void LongestSequence(int fre[][MAX_CHAR], int n)
{
    // to get lexicographical largest sequence.
    for (int i = MAX_CHAR-1; i >= 0; i--) {
 
        // find minimum of that character
        int mi = fre[0][i];
        for (int j = 1; j < n; j++)
            mi = min(fre[j][i], mi);       
 
        // print that character
        // minimum number of times
        while (mi--)
            cout << (char)('a' + i);       
    }
}
 
// Driver code
int main()
{
 
    string s[] = { "loo", "lol", "olive" };
    int n = sizeof(s)/sizeof(s[0]);
 
    // to store frequency of each character in each string
    int fre[n][26] = { 0 };
 
    // to get frequency of each character
    frequency(fre, s, n);
 
    // function call
    LongestSequence(fre, n);
 
    return 0;
}

Java

// Java program to find longest
// possible subsequence anagram
// of N strings.
class GFG
{
final int MAX_CHAR = 26;
 
// function to store frequency
// of each character in each
// string
static void frequency(int fre[][],
                      String s[], int n)
{
    for (int i = 0; i < n; i++)
    {
        String str = s[i];
        for (int j = 0;
                 j < str.length(); j++)
            fre[i][str.charAt(j) - 'a']++;    
    }
}
 
// function to Find longest
// possible sequence of N
// strings which is anagram
// to each other
static void LongestSequence(int fre[][],
                            int n)
{
    // to get lexicographical
    // largest sequence.
    for (int i = 24; i >= 0; i--)
    {
 
        // find minimum of
        // that character
        int mi = fre[0][i];
        for (int j = 1; j < n; j++)
            mi = Math.min(fre[j][i], mi);    
 
        // print that character
        // minimum number of times
        while (mi--!=0)
            System.out.print((char)('a' + i));    
    }
}
 
// Driver code
public static void main(String args[])
{
 
    String s[] = { "loo", "lol", "olive" };
    int n = s.length;
 
    // to store frequency of each
    // character in each string
    int fre[][] = new int[n][26] ;
 
    // to get frequency
    // of each character
    frequency(fre, s, n);
 
    // function call
    LongestSequence(fre, n);
}
}
 
// This code is contributed
// by Arnab Kundu

Python3

# Python3 program to find longest possible
# subsequence anagram of N strings.
 
# Function to store frequency of
# each character in each string
def frequency(fre, s, n):
 
    for i in range(0, n):
        string = s[i]
        for j in range(0, len(string)):
            fre[i][ord(string[j]) - ord('a')] += 1       
 
# Function to Find longest possible sequence 
# of N strings which is anagram to each other
def LongestSequence(fre, n):
 
    # to get lexicographical largest sequence.
    for i in range(MAX_CHAR-1, -1, -1):
 
        # find minimum of that character
        mi = fre[0][i]
        for j in range(1, n):
            mi = min(fre[j][i], mi)        
 
        # print that character
        # minimum number of times
        while mi:
            print(chr(ord('a') + i), end = "")
            mi -= 1
     
# Driver code
if __name__ == "__main__":
 
    s = ["loo", "lol", "olive"]
    n = len(s)
    MAX_CHAR = 26
 
    # to store frequency of each
    # character in each string
    fre = [[0 for i in range(26)]
              for j in range(n)]
 
    # To get frequency of each character
    frequency(fre, s, n)
 
    # Function call
    LongestSequence(fre, n)
 
# This code is contributed by
# Rituraj Jain

C#

// c# program to find longest
// possible subsequence anagram
// of N strings.
using System;
 
class GFG
{
public readonly int MAX_CHAR = 26;
 
// function to store frequency
// of each character in each
// string
public static void frequency(int[,] fre,
                             string[] s, int n)
{
    for (int i = 0; i < n; i++)
    {
        string str = s[i];
        for (int j = 0;
                 j < str.Length; j++)
        {
            fre[i, str[j] - 'a']++;
        }
    }
}
 
// function to Find longest
// possible sequence of N
// strings which is anagram
// to each other
public static void LongestSequence(int[, ] fre,
                                   int n)
{
    // to get lexicographical
    // largest sequence.
    for (int i = 24; i >= 0; i--)
    {
 
        // find minimum of
        // that character
        int mi = fre[0, i];
        for (int j = 1; j < n; j++)
        {
            mi = Math.Min(fre[j, i], mi);
        }
 
        // print that character
        // minimum number of times
        while (mi--!=0)
        {
            Console.Write((char)('a' + i));
        }
    }
}
 
// Driver code
public static void Main(string[] args)
{
 
    string[] s = new string[] {"loo", "lol", "olive"};
    int n = s.Length;
 
    // to store frequency of each
    // character in each string
    int[, ] fre = new int[n, 26];
 
    // to get frequency
    // of each character
    frequency(fre, s, n);
 
    // function call
    LongestSequence(fre, n);
}
}
 
// This code is contributed by Shrikanth13

Javascript

<script>
 
// JavaScript program to find longest
// possible subsequence anagram
// of N strings.
 
let MAX_CHAR = 26;
 
// function to store frequency
// of each character in each
// string
function frequency(fre,s,n)
{
    for (let i = 0; i < n; i++)
    {
        let str = s[i];
        for (let j = 0;
                 j < str.length; j++)
            fre[i][str[j].charCodeAt(0) - 'a'.charCodeAt(0)]++;   
    }
}
 
// function to Find longest
// possible sequence of N
// strings which is anagram
// to each other
function LongestSequence(fre,n)
{
    // to get lexicographical
    // largest sequence.
    for (let i = 24; i >= 0; i--)
    {
  
        // find minimum of
        // that character
        let mi = fre[0][i];
        for (let j = 1; j < n; j++)
            mi = Math.min(fre[j][i], mi);   
  
        // print that character
        // minimum number of times
        while (mi--!=0)
            document.write(String.fromCharCode
            ('a'.charCodeAt(0) + i));   
    }
}
 
// Driver code
let s=["loo", "lol", "olive"];
let n = s.length;
  
// to store frequency of each
// character in each string
let fre = new Array(n) ;
for(let i=0;i<n;i++)
{
    fre[i]=new Array(26);
    for(let j=0;j<26;j++)
        fre[i][j]=0;
}
 
// to get frequency
// of each character
frequency(fre, s, n);
 
// function call
LongestSequence(fre, n);
 
// This code is contributed by avanitrachhadiya2155
 
</script>

Output:

ol

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