Valid Number

Validate if a given string can be interpreted as a decimal number.

Some examples: "0" => true " 0.1 " => true "abc" => false "1 a" => false "2e10" => true " -90e3 " => true " 1e" => false "e3" => false " 6e-1" => true " 99e2.5 " => false "53.5e93" => true " --6 " => false "-+3" => false "95a54e53" => false

Note: It is intended for the problem statement to be ambiguous. You should gather all requirements up front before implementing one. However, here is a list of characters that can be in a valid decimal number:

• Numbers 0-9

• Exponent - "e"

• Positive/negative sign - "+"/"-"

• Decimal point - "."

Of course, the context of these characters also matters in the input.

class Solution {
    public boolean isNumber(String s) {
        s = s.trim();
        boolean pointSeen = false;
        boolean eSeen = false;
        boolean numberSeen = false;
        for (int i = 0; i < s.length(); i++) {
            if ('0' <= s.charAt(i) && s.charAt(i) <= '9')
                numberSeen = true;
            else if (s.charAt(i) == '.') {
                if (eSeen || pointSeen)
                    return false;
                pointSeen = true;
            } else if (s.charAt(i) == 'e') {
                if (eSeen || !numberSeen)
                    return false;
                numberSeen = false;
                eSeen = true;
            } else if (s.charAt(i) == '-' || s.charAt(i) == '+') {
                if (i != 0 && s.charAt(i - 1) != 'e')
                    return false;
            } else
                return false;
        }
        return numberSeen;
    }
}