第28题 Valid Number

验证数值型字符串

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本文介绍了一种使用正则表达式的方法来判断一个给定的字符串是否代表一个有效的数字，包括整数、小数和科学计数法形式。通过具体的代码实现，文章详细解释了如何处理各种边界情况。

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.

Solution in Java：

public class Solution {
    public boolean isNumber(String s) {
        String sTrim = s.trim();
        if(sTrim.length()==0) return false;
        if(sTrim.contains(" ")) return false;
        
        String pattern1 = "", pattern2 = "";
        if(sTrim.contains("e")){
            int indexE = sTrim.indexOf('e');
            String beforeE="", afterE="";
            if(indexE!=-1){
                beforeE = sTrim.substring(0,indexE);
                afterE = sTrim.substring(indexE+1, sTrim.length());
                indexE = sTrim.indexOf('e', indexE+1);
                if(indexE!=-1) return false;
            }
            pattern1 = "^[+,-]?[0-9]+$";
            if(!afterE.matches(pattern1)) 
                return false;
            if(beforeE.contains(".")){
                pattern1 = "^[+,-]?[0-9]*[.]{1}[0-9]+$";
                pattern2 = "^[+,-]?[0-9]+[.]{1}[0-9]*$";
                if(beforeE.matches(pattern1)||beforeE.matches(pattern2)) return true;
                else return false;
            }else{
                pattern1 = "^[+,-]?[0-9]+$";
                if(beforeE.matches(pattern1)) return true;
                else return false;
            }
        }
        else{
            if(sTrim.contains(".")){
                pattern1 = "^[+,-]?[0-9]+[.]{1}[0-9]*$";
                pattern2 = "^[+,-]?[0-9]*[.]{1}[0-9]+$";
                if(sTrim.matches(pattern1)||sTrim.matches(pattern2)) return true;
                else return false;
            }
            else{
                pattern1 = "^[+,-]?[0-9]+$";
                if(sTrim.matches(pattern1)) return true;
                else return false;
            }
    }
}

Note：

“.3”也算valid number！"3."也算valid number！但"."前后不可同时为空字符，所以要用或判断。

"7e69e"在java中用split分割，长度为2，最后不算第二个e后的空字符，所以不能检查如“e123e”格式的字符串。所以用indexOf函数查找字符"e"，然后用substring获取"e"前后字符。string.indexOf('e',index)查找从string的index位置开始有无字符'e'。

科学计数法e后可以加＋或－号，后面跟数字。