public static int palindromeIndex(string s)
{
    for (int i = 0, j = s.Length - 1; i < j; i++, j--)
    {
        if (s[i] != s[j])
        {
            // remove 1 char at i or j
            // then check for condition
            // if false -> do not need to check the remain positions
            // because it can not be palindrome anymore
            // return -1
            if (CheckPalindrome(s, i + 1, j)) return i; //remove at position i & check
            if (CheckPalindrome(s, i, j - 1)) return j; //remove at position j & check
            return -1; // there is no solution
        }
    }
    return -1; // it's palindrome already  
}
public static bool CheckPalindrome(string s, int left, int right)
{
    for (int i = left, j = right; i < j; i++, j--)
    {
        if (s[i] != s[j]) return false;
    }
    return true;

}