Valid Number

Validate if a given string is numeric.

Example

"0" => true

" 0.1 " => true

"abc" => false

"1 a" => false

"2e10" => true

 

考察 corner case

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