Given two strings check which string makes a palindrome first

Given two strings ‘A’ and ‘B’ of equal length. Two players play a game where they both pick a character from their respective strings (First picks from A and second from B) and put into a third string (which is initially empty). The player that can make the third string palindrome, is winner. If first player makes palindrome first then print ‘A’, else ‘B’. If strings get empty and no one is able to make a palindrome, then print ‘B’. 

Examples:

Input : A = ab
        B = ab
Output : B
First player puts 'a' (from string A)
Second player puts 'a' (from string B) 
which make palindrome. 
The result would be same even if A picks
'b' as first character.

Input : A = aba
        B = cde
Output : A

Input : A = ab
        B = cd
Output : B
None of the string will be able to
make a palindrome (of length > 1)
in any situation. So B will win.

After taking few examples, we can observe that ‘A’ (or first player) can only win when it has a character that appears more than once and not present in ‘B’. 

Implementation:

C++

// Given two strings, check which string
// makes palindrome first.
#include<bits/stdc++.h>
using namespace std;

const int MAX_CHAR = 26;

// returns winner of two strings
char stringPalindrome(string A, string B)
{
    // Count frequencies of characters in
    // both given strings
    int countA[MAX_CHAR] = {0};
    int countB[MAX_CHAR] = {0};
    int l1 = A.length(), l2 = B.length();
    for(int i=0; i<l1;i++)
        countA[A[i]-'a']++;
    for(int i=0; i<l2;i++)
        countB[B[i]-'a']++;

    // Check if there is a character that
    // appears more than once in A and does
    // not appear in B
    for (int i=0 ;i <26;i++)
        if ((countA[i] >1 && countB[i] == 0))
           return 'A';

    return 'B';
}

// Driver Code
int main()
{
    string a = "abcdea";
    string b = "bcdesg";
    cout << stringPalindrome(a,b);
    return 0;
}

Java

// Java program to check which string
// makes palindrome first.
public class First_Palin {

    static final int MAX_CHAR = 26;

    // returns winner of two strings
    static char stringPalindrome(String A, String B)
    {
        // Count frequencies of characters in
        // both given strings
        int[] countA = new int[MAX_CHAR];
        int[] countB = new int[MAX_CHAR];

        int l1 = A.length();
        int l2 = B.length();

        for (int i = 0; i < l1; i++)
            countA[A.charAt(i) - 'a']++;

        for (int i = 0; i < l2; i++)
            countB[B.charAt(i) - 'a']++;

        // Check if there is a character that
        // appears more than once in A and does
        // not appear in B
        for (int i = 0; i < 26; i++)
            if ((countA[i] > 1 && countB[i] == 0))
                return 'A';

        return 'B';
    }

    // Driver Code
public static void main(String args[])
    {
        String a = "abcdea";
        String b = "bcdesg";
        System.out.println(stringPalindrome(a, b));
    }
}
// This code is contributed by Sumit Ghosh

Python3

# Given two strings, check which string
# makes palindrome first.

MAX_CHAR = 26

# returns winner of two strings
def stringPalindrome(A, B):

    # Count frequencies of characters
    # in both given strings
    countA = [0] * MAX_CHAR
    countB = [0] * MAX_CHAR
    l1 = len(A)
    l2 = len(B)
    for i in range(l1):
        countA[ord(A[i]) - ord('a')] += 1
    for i in range(l2):
        countB[ord(B[i]) - ord('a')] += 1

    # Check if there is a character that
    # appears more than once in A and
    # does not appear in B
    for i in range(26):
        if ((countA[i] > 1 and countB[i] == 0)):
            return 'A'
    return 'B'

# Driver Code
if __name__ == '__main__':
    a = "abcdea"
    b = "bcdesg"
    print(stringPalindrome(a, b))

# This code is contributed by Rajput-Ji

C#

// C# program to check which string
// makes palindrome first.
using System;

class First_Palin {

    static int MAX_CHAR = 26;

    // returns winner of two strings
    static char stringPalindrome(string A, string B)
    {
        // Count frequencies of characters in
        // both given strings
        int[] countA = new int[MAX_CHAR];
        int[] countB = new int[MAX_CHAR];

        int l1 = A.Length;
        int l2 = B.Length;

        for (int i = 0; i < l1; i++)
            countA[A[i] - 'a']++;

        for (int i = 0; i < l2; i++)
            countB[B[i] - 'a']++;

        // Check if there is a character that
        // appears more than once in A and does
        // not appear in B
        for (int i = 0; i < 26; i++)
            if ((countA[i] > 1 && countB[i] == 0))
                return 'A';

        return 'B';
    }

    // Driver Code
    public static void Main()
    {
        string a = "abcdea";
        string b = "bcdesg";
    Console.WriteLine(stringPalindrome(a, b));
    }
}

// This code is contributed by vt_m.

PHP

<?php
// Given two strings, check which string
// makes palindrome first.

$MAX_CHAR = 26;

// returns winner of two strings
function stringPalindrome($A, $B)
{
    global $MAX_CHAR;

    // Count frequencies of characters in
    // both given strings
    $countA = array_fill(0, $MAX_CHAR, 0);
    $countB = array_fill(0, $MAX_CHAR, 0);
    $l1 = strlen($A);
    $l2 = strlen($B);
    for($i = 0; $i < $l1; $i++)
        $countA[ord($A[$i])-ord('a')]++;
    for($i = 0; $i < $l2; $i++)
        $countB[ord($B[$i])-ord('a')]++;

    // Check if there is a character that
    // appears more than once in A and does
    // not appear in B
    for ($i = 0 ; $i < 26; $i++)
        if (($countA[$i] > 1 && $countB[$i] == 0))
        return 'A';

    return 'B';
}

    // Driver Code
    $a = "abcdea";
    $b = "bcdesg";
    echo stringPalindrome($a,$b);

// This code is contributed by mits
?>

Javascript

<script>

// javascript program to check which string
// makes palindrome first.


    var MAX_CHAR = 26;

    // returns winner of two strings
    function stringPalindrome(A, B)
    {
        // Count frequencies of characters in
        // both given strings
        var countA = Array.from({length: MAX_CHAR}, (_, i) => 0);
        var countB = Array.from({length: MAX_CHAR}, (_, i) => 0);

        var l1 = A.length;
        var l2 = B.length;

        for (var i = 0; i < l1; i++)
            countA[A.charAt(i).charCodeAt(0) - 'a'.charCodeAt(0)]++;

        for (var i = 0; i < l2; i++)
            countB[B.charAt(i).charCodeAt(0) - 'a'.charCodeAt(0)]++;

        // Check if there is a character that
        // appears more than once in A and does
        // not appear in B
        for (var i = 0; i < 26; i++)
            if ((countA[i] > 1 && countB[i] == 0))
                return 'A';

        return 'B';
    }

    // Driver Code
    var a = "abcdea";
    var b = "bcdesg";
    document.write(stringPalindrome(a, b));

// This code is contributed by 29AjayKumar
</script>

Output

A

Time complexity: O(l1+l2)
Auxiliary space: O(52)