Minimum number of Appends needed to make a string palindrome

2.6

Given a string s we need to tell minimum characters to be appended (insertion at end) to make a string palindrome.

Examples:

Input : s = "abede"
Output : 2
We can make string palindrome as "abedeba"
by adding ba at the end of the string.

Input : s = "aabb"
Output : 2
We can make string palindrome as"aabbaa"
by adding aa at the end of the string.

The solution can be achieved by removing characters from the beginning of the string one by one and checking if the string is palindrome or not.

For Example, consider the above string, s = “abede”.

We check if the string is palindrome or not.

The result is false, then we remove the character from the beginning of string and now string becomes “bede”.

We check if the string is palindrome or not. The result is again false, then we remove the character from the beginning of string and now string becomes “ede”.

We check if the string is palindrome or not. The result is true, so the output becomes 2 which is the number of characters removed from the string.

// C program to find minimum number of appends
// needed to make a string Palindrome
#include<stdio.h>
#include<string.h>
#include<stdbool.h>

// Checking if the string is palindrome or not
bool isPalindrome(char *str)
{
    int len = strlen(str);

    // single character is always palindrome
    if (len == 1)
        return true;

    // pointing to first character
    char *ptr1 = str;

    // pointing to last character
    char *ptr2 = str+len-1;

    while (ptr2 > ptr1)
    {
        if (*ptr1 != *ptr2)
            return false;
        ptr1++;
        ptr2--;
    }

    return true;
}

// Recursive function to count number of appends
int noOfAppends(char s[])
{
    if (isPalindrome(s))
        return 0;

    // Removing first character of string by
    // incrementing base address pointer.
    s++;

    return 1 + noOfAppends(s);
}

// Driver program to test above functions
int main()
{
    char s[] = "abede";
    printf("%d\n", noOfAppends(s));
    return 0;
}

Output:

2

Related Article :
Dynamic Programming | Set 28 (Minimum insertions to form a palindrome)

This article is contributed by Shubham Chaudhary. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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