# Find a palindromic string B such that given String A is a subsequense of B

Given a string . Find a string , where B is a palindrome and A is a subsequence of B.

A subsequence of a string is a string that can be derived from it by deleting some (not necessarily consecutive) characters without changing the order of the remaining characters. For example, “cotst” is a subsequence of “contest”.

A palindrome is a string that reads the same forward or backward.

Examples:

Input : A = "aba"
Output : B = aba
Explanation : "aba" is a subsequence of "aba"
which is a palindrome.

Input : A = "ab"
Output : B = abba

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

Approach: Let reverse(s) be the reverse of a string . Now, s + reverse(s) will always have as a subsequence (as first half) and it is a palindrome.

Therefore, B = A + reverse(A).

Below is the implementation of the above approach:

## C++

 // C++ program to find a palindromic string B // such that given String A is a subsequense of B #include using namespace std;    // Function to check if a string is palindrome bool checkPalindrome(string s) {     // Reversing a string     string x = s;     reverse(s.begin(), s.end());        // check if reversed string is equal     // to given string     return s == x; }    // Function to find a palindromic string B // such that given String A is a subsequense of B string findStringB(string A) {     // Reversing the string A     string B = A;     reverse(A.begin(), A.end());     A = A + B;        // If the string A is already a palindrome     // return A     if (checkPalindrome(B))         return B;        // else return B     return A; }    string reverse(string input) {     string temparray = input;     int left, right = 0;     right = temparray.length() - 1;        for (left = 0; left < right; left++, right--)            // Swap values of left and right         swap(temparray[left], temparray[right]);        return temparray; }    // Driver Code int main(int argc, char const *argv[]) {     string A = "ab";     cout << findStringB(A) << endl;     return 0; }    // This code is contributed by // sanjeev2552

## Java

 // Java program to find a palindromic string B // such that given String A is a subsequense of B    class GFG  {        // Function to check if a string is palindrome     static boolean checkPalindrome(String s)      {         // Reversing a string         String x = reverse(s);                    // check if reversed string is equal          // to given string         return x.equals(s);     }            // Function to find a palindromic string B     // such that given String A is a subsequense of B     static String findStringB(String A)      {            // Reversing the string A         String B = reverse(A);         B = B + A;            // If the string A is already a palindrome         // return A         if (checkPalindrome(A))          {             return A;         }            // else return B          return B;     }        static String reverse(String input)     {         char[] temparray = input.toCharArray();         int left, right = 0;         right = temparray.length - 1;            for (left = 0; left < right; left++, right--)          {             // Swap values of left and right              char temp = temparray[left];             temparray[left] = temparray[right];             temparray[right] = temp;         }         return String.valueOf(temparray);     }            // Driver Code     public static void main(String[] args)      {         String A = "ab";         System.out.println(findStringB(A));     } }    // This code contributed by Rajput-Ji

## Python

 # Python program to find a palindromic string B # such that given String A is a subsequense of B    # Function to check if a string is palindrome def checkPalindrome(s):     # Reversing a string     x = s[::-1]     # check if reversed string is equal      # to given string     if(x == s):         return True     else:         return False            # Function to find a palindromic string B # such that given String A is a subsequense of B def findStringB(A):            # Reversing the string A     B = A[::-1]            B = B + A            # If the string A is already a palindrome     # return A     if(checkPalindrome(A)):         return A              # else return B         return B    # Driver Code A ="ab" print(findStringB(A))

## C#

 // C# program to find a palindromic string B // such that given String A is a subsequense of B using System;    class GFG  {         // Function to check if a string is palindrome     static bool checkPalindrome(String s)      {         // Reversing a string         String x = reverse(s);                     // check if reversed string is equal          // to given string         return x.Equals(s);     }             // Function to find a palindromic string B     // such that given String A is a subsequense of B     static String findStringB(String A)      {             // Reversing the string A         String B = reverse(A);         B = B + A;             // If the string A is already a palindrome         // return A         if (checkPalindrome(A))          {             return A;         }             // else return B          return B;     }         static String reverse(String input)     {         char[] temparray = input.ToCharArray();         int left, right = 0;         right = temparray.Length - 1;             for (left = 0; left < right; left++, right--)          {             // Swap values of left and right              char temp = temparray[left];             temparray[left] = temparray[right];             temparray[right] = temp;         }         return String.Join("",temparray);     }             // Driver Code     public static void Main(String[] args)      {         String A = "ab";         Console.WriteLine(findStringB(A));     } }    // This code has been contributed by 29AjayKumar

Output:

baab

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