Find longest palindrome and its length in a given string using C?

Question

Given a string, add some characters to the from of it so that it becomes a palindrome.
e.g.
1) If input is "abc" then "bcabc" should be returned.
2) input -> "ab" output -> "bab"
3) input -> "a" output -> "a"

Answer 1

The program to find Longest Palindrome and its length in a given string:- (Try this code)

#include <stdio.h>
#include <string.h>

// A utility function to print a substring str[low..high]
void printSubStr(char* str, int low, int high)
{
    for( int i = low; i <= high; ++i )
        printf("%c", str[i]);
}

// This function prints the longest palindrome substring (LPS)
// of str[]. It also returns the length of the longest palindrome
int longestPalSubstr(char *str)
{
    int maxLength = 1;  // The result (length of LPS)

    int start = 0;
    int len = strlen(str);

    int low, high;

    // One by one consider every character as center point of 
    // even and length palindromes
    for (int i = 1; i < len; ++i)
    {
        // Find the longest even length palindrome with center points
        // as i-1 and i.  
        low = i - 1;
        high = i;
        while (low >= 0 && high < len && str[low] == str[high])
        {
            if (high - low + 1 > maxLength)
            {
                start = low;
                maxLength = high - low + 1;
            }
            --low;
            ++high;
        }

        // Find the longest odd length palindrome with center 
        // point as i
        low = i - 1;
        high = i + 1;
        while (low >= 0 && high < len && str[low] == str[high])
        {
            if (high - low + 1 > maxLength)
            {
                start = low;
                maxLength = high - low + 1;
            }
            --low;
            ++high;
        }
    }

    printf("Longest palindrome substring is: ");
    printSubStr(str, start, start + maxLength - 1);

    return maxLength;
}

// Driver program to test above functions
int main()
{
    char str[] = "forgeeksskeegfor";
    printf("\nLength is: %d\n", longestPalSubstr( str ) );
    return 0;
}