[leetcode] Valid Number

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.

https://oj.leetcode.com/problems/valid-number/

思路1：直接处理，一般思路按照'.’分开整数和小数，然后各自判断，情况略复杂。

思路2：自动机，建立好转移函数，代码很直观易懂。

思路3（偷懒）：直接写正则表达式（其实正则的匹配背后也是自动机）。

public class Solution {
    public boolean isNumber(String s) {
        if (s.trim().isEmpty()) {
            return false;
        }
        String regex = "[-+]?(\d+\.?|\.\d+)\d*(e[-+]?\d+)?";
        if (s.trim().matches(regex)) {
            return true;
        } else {
            return false;
        }
    }

    public static void main(String[] args) {
        System.out.println(new Solution().isNumber("0"));
        System.out.println(new Solution().isNumber("0.1"));
        System.out.println(new Solution().isNumber(".1"));
        System.out.println(new Solution().isNumber("0."));
        System.out.println(new Solution().isNumber("."));
        System.out.println(new Solution().isNumber("abc"));
        System.out.println(new Solution().isNumber("1 a"));
        System.out.println(new Solution().isNumber("2e10"));
    }
}

参考：

http://jane4532.blogspot.com/2013/09/valid-numberleetcode.html

http://www.cnblogs.com/chasuner/p/validNumber.html

http://leetcodenotes.wordpress.com/2013/11/23/leetcode-valid-number/
http://codeganker.blogspot.com/2014/04/valid-number-leetcode.html