Cassido's weekly interview problem (2/10/19)

charsToPalindrome.java

/**
 * Created by Kyle Long on 2/12/19.
 */
public class charsToPalindrome {
    public static void main(String [] args){
        String s = "hi"; //hi -> hih or ihi
        String s1 = "xx"; //already palindrome
        String s2 = "race"; //racecar
        String s3 = "abcdabc"; //not possible to convert into a palindrome
        System.out.println(makeAPal(s));
        System.out.println(makeAPal(s1));
        System.out.println(makeAPal(s2));
        System.out.println(makeAPal(s3));

    }

    /**
     * Finds the minimum number of characters to be inserted to
     * convert it to palindrome.
     * @param s String to covert to potentially convert to a palindrome
     * @return num of characters needed to be added to make it a palindrome
     */
    public static int makeAPal(String s){
        //already palindrome
        if(isPalindrome(s)) return 0;
        StringBuilder sb = new StringBuilder(s);
        int count = 0;
        int offset = (s.length() / 2 % 2) == 0 ? 0: 1;
        for(int i = (s.length() / 2 ) - offset; i >= 0; i--){
            sb.append(s.charAt(i));
            count++;
            if(isPalindrome(sb.toString())){
                return count;
            }
        }
        return -1; //not possible

    }

    /**
     * Checks if a string is a palindrome
     * @param s String to check if it is a palindrome
     * @return if is a palindrome
     */
    public static boolean isPalindrome(String s){
        char [] arr = s.toCharArray();
        int length = arr.length;
        for(int i = 0; i < length / 2; i++){
            if(arr[i] != arr[length - 1 - i]){
                return false;
            }
        }
        return true;

    }
}