FB面经 Prepare: All Palindromic Substrings

Given a string, calculate how many substring is palindrome. Ignore non-char characters. Ignore case;

Ex: "A@,b123a", equals "Aba", should output 4: "A", "b", "a", "Aba"

Spread from center: Like LC 5: longest palindromic substring

package fb;

public class Palindrome {
    public int countSubStr(String input) {
        if (input==null || input.length()==0) return 0;
        int res = 0;
        for (int i=0; i<input.length(); i++) {
            if (!isAlpha(input, i)) continue;
            res += helper(input, i, i);
            if (i < input.length()-1) res += helper(input, i, i+1);
        }
        return res;
    }
    
    public int helper(String s, int l, int r) {
        int res = 0;
        while (l>=0 && r<s.length()) {
            while (l>=0 && !isAlpha(s, l)) l--;
            while (r<s.length() && !isAlpha(s, r)) r++;
            if (l<0 || r>=s.length() || !isSame(s, l, r)) break;
            else {
                res++;
                l--;
                r++;
            }
        }
        return res;
    }
    
    public boolean isAlpha(String s, int i) {
        char c = s.charAt(i);
        if (c>='a' && c<='z' || c>='A' && c<='Z') return true;
        return false;
    }
    
    public boolean isSame(String s, int l, int r) {
        char ll = s.charAt(l);
        char rr = s.charAt(r);
        ll = Character.isUpperCase(ll)? (char)(ll-'A'+'a') : ll;
        rr = Character.isUpperCase(rr)? (char)(rr-'A'+'a') : rr;
        return ll==rr;
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Palindrome sol = new Palindrome();
        String input = "A@,b123a";
        //String input = "Aba";
        int res = sol.countSubStr(input);
        System.out.println(res);

    }

}