65. Valid Number

class Solution {
    public boolean isNumber(String s) {
        if(s == null) return false;
        s = s.trim();
        if(s.length() < 1) return false;
        for(char ch : s.toCharArray())
        {
            if(Character.isDigit(ch) || ch == '.' || ch == 'e' || ch == '+' || ch == '-') continue;
            return false;   // invalid for any other characters
        }
        // now try to separate s into two parts
        int pos = s.indexOf('e');
        if(pos < 0) return parseD(s) || parseI(s);
        String sub1 = s.substring(0, pos), sub2 = s.substring(pos + 1);
        int l1 = sub1.length(), l2 = sub2.length();
        if(l1 < 1 || l2 < 1) return false;
        return (parseD(sub1) || parseI(sub1)) && parseI(sub2);
    }

    boolean parseD(String s)
    {
        int pos = s.indexOf('.');
        if(pos < 0)
        {
            return parseI(s);
        }
        // has dot
        /*
        possible forms
        [sign] #.#
        [] #.EMPTY
        []EMPTY.#
        */
        String sub1 = s.substring(0, pos), sub2 = s.substring(pos + 1);
        int l1 = sub1.length(), l2 = sub2.length();
        if(l1 < 1 && l2 < 1) return false;  // EMPTY.EMPTY
        if(l2 < 1) return parseI(sub1); // [sign]#.EMPTY
        return sub1.matches("[+|-]?[\\d]*") && parseI0(sub2);    // [sign]Empty.#
    }

    boolean parseI(String s)
    {
        // if(s.length() < 1) return true;
        if(s.charAt(0) == '+' || s.charAt(0) == '-') s = s.substring(1);
        return parseI0(s);
    }

    boolean parseI0(String s)
    {
        // System.out.println(s);
        // System.out.println(s.matches("\\d+"));
        return s.matches("\\d+");
    }
}