Valid Number

Source

• lintcode: Valid Number

Validate if a given string is numeric.

Example
"0" => true

" 0.1 " => true

"abc" => false

"1 a" => false

"2e10" => true

Java

public class Solution {
    /**
     * @param s the string that represents a number
     * @return whether the string is a valid number
     */
    public boolean isNumber(String s) {
        int len = s.length();
        int i = 0, e = len - 1;
        while (i <= e && Character.isWhitespace(s.charAt(i))) i++;
        if (i > len - 1) return false;
        while (e >= i && Character.isWhitespace(s.charAt(e))) e--;
        // skip leading +/-
        if (s.charAt(i) == '+' || s.charAt(i) == '-') i++;
        boolean num = false; // is a digit
        boolean dot = false; // is a '.'
        boolean exp = false; // is a 'e'
        while (i <= e) {
            char c = s.charAt(i);
            if (Character.isDigit(c)) {
                num = true;
            }
            else if (c == '.') {
                if(exp || dot) return false;
                dot = true;
            }
            else if (c == 'e') {
                if(exp || num == false) return false;
                exp = true;
                num = false;
            }
            else if (c == '+' || c == '-') {
                if (s.charAt(i - 1) != 'e') return false;
            }
            else {
                return false;
            }
            i++;
        }
        return num;
    }
}