// java solution

private static int findIndexOfMismatch(String s) { for(int i=0 ; i

public static int palindromeIndex(String s) {
    int mismatchIndex = findIndexOfMismatch(s);
    if(mismatchIndex==-1) {
        // is already a palindrome
        return -1;
    }

    // option 1 - remove mismatching char at the left and check
    String maybePalindrome = s.substring(mismatchIndex+1, s.length()-mismatchIndex);
    if(findIndexOfMismatch(maybePalindrome)==-1) {
        return mismatchIndex;
    }

    // option 2 - remove mismatching char at the right and check
    maybePalindrome = s.substring(mismatchIndex, s.length()-mismatchIndex-1);
    if(findIndexOfMismatch(maybePalindrome)==-1) {
        return s.length()-mismatchIndex-1;
    }

    // option 3 - removing one char is not enough to make this into a palindrome
    return -1;
}