Validate if a given string is numeric.

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

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

原题链接：https://oj.leetcode.com/problems/valid-number/

判断字符串是否是数字。

规则：出现+, - 则必须是第一个，或前一个是e；有. 则是小数，之前不可有.和e；有e，则前面要有.，不能有e，并且后面要有.。

可用正则表达式来解答。

	public static boolean isNumber(String s) {
		String reg = "[+-]?(\\d+\\.?|\\.\\d+)\\d*(e[+-]?\\d+)?";
		return s.trim().matches(reg);
	}

LeetCode——Valid Number