1. Description

Validate if a given string is numeric.

Note: It is intended for the problem statement to be ambiguous. You should gather all requirements up front before implementing one.

2. Example

"0" => true
" 0.1 " => true
"abc" => false
"1 a" => false
"2e10" => true

3.Code

public class LeetCode0065 {

    public boolean isNumber(String s) {
        if (s == null) {
            return false;
        }

        s = s.trim();

        if (s.length() == 0) {
            return false;
        }

        s = removeSign(s);

        if (s.length() == 0) {
            return false;
        }

        if(s.length() == 1 && !Character.isDigit(s.charAt(0))) {
            return false;
        }

        if(s.contains("e")) {
            return handleE(s);
        }

        return handlePoint(s);
    }

    private String removeSign(String s) {
        if(s.charAt(0) == '+' || s.charAt(0) == '-') {
            s = s.substring(1, s.length());
        }
        return s;
    }


    private boolean handlePoint(String s) {
        for(int i = 0; i< s.length(); i++) {
            char c = s.charAt(i);
            if(!Character.isDigit(c) && c != '.') {
                return false;
            }
        }

        int pIndex = s.indexOf('.');
        if(pIndex == -1) {
            return true;
        }

        if(s.lastIndexOf('.') != pIndex) {
            return false;
        }

        if(pIndex == 0 || pIndex == s.length() -1) {
            if(s.length() == 1) {
                return false;
            }
        }
        return true;
    }

    private boolean handleE(String s) {

        int eIndex = s.indexOf('e');
        if(s.lastIndexOf('e') != eIndex) {
            return false;
        }

        String base = s.substring(0, eIndex);
        String power = s.substring(eIndex + 1, s.length());

        if(base.length() == 0) {
            return false;
        }

        if(power.length() == 0) {
            return false;
        }

        power = removeSign(power);

        if(power.length() == 0) {
            return false;
        }

        for(int i = 0; i< power.length();i++) {
            if(!Character.isDigit(power.charAt(i))) {
                return false;
            }
        }

        return handlePoint(base);   
    }

    public static void main(String[] args) {
        LeetCode0065 leetcode = new LeetCode0065();
        System.out.println(leetcode.isNumber("2e0"));
    }
}