[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"));
}
}

View Code

参考：

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

/article/5904219.html

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