Valid Number

class Solution {
    public boolean isNumber(String s) {
        if (s == null)return false;
        s = s.trim();
        if (s.length() == 0) return false;
        boolean point = false, sign = false, exponent = false, number = false;
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            if (!Character.isDigit(c)) {
                if (c != 'e' && c != '+' && c != '-' && c != '.') return false;
                if (c == '.') {
                    if (point) {
                        return false;
                    } else if (exponent) {
                        return false;
                    } else {
                        point = true;
                    }
                }
                if (c == 'e') {
                    if (exponent) return false;
                    if (!number) return false;
                    exponent = true;
                    number = false;
                }
                if (c == '+' || c == '-') {
                    if (i == 0) {
                        sign = true;
                    } else {
                        if (s.charAt(i - 1) != 'e') return false;
                    }
                }
            } else {
                number = true;
            }
        }
        return number;
    }
}