Valid Number

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.

public class Solution {
    public boolean isNumber(String s) {
        boolean result = true;
        s = s.trim();//去掉前面和后面的空格
        if(0 != s.length() && (s.charAt(0) == '+' || s.charAt(0) == '-'))
            s = s.substring(1, s.length());
        if(0 == s.length())
            return false;
        boolean flag_point = false;
        boolean flag_e = false;//记录小数点和字母e
        
        
        for(int i = 0; i < s.length(); i++){
            char ch = s.charAt(i);//第i个字符
            if('.' == ch){                
                if(flag_e || flag_point || !((i + 1 < s.length() && s.charAt(i + 1) >= '0' && s.charAt(i + 1) <= '9')||
                    (i - 1 >= 0 && s.charAt(i - 1) >= '0' && s.charAt(i - 1) <= '9'))//e出现过就不能出现小数点了
                    )
                {
                    return false;
                }
                flag_point = true;
            }//小数点后面或者前面有数字即可
            if('e' == ch){                                    
                if(flag_e || 
                        !((i + 1 < s.length() && (s.charAt(i + 1) >= '0' && s.charAt(i + 1) <= '9' || s.charAt(i + 1) == '+'|| s.charAt(i + 1) == '-'))&&
                                (i - 1 >= 0 && (s.charAt(i - 1) >= '0' && s.charAt(i - 1) <= '9' || s.charAt(i - 1) == '.'))))
                {
                    return false;
                }
                flag_e = true;
            }//小数点和e的个数
            if(flag_e && (ch == '+' || ch == '-')){
                if(!(s.charAt(i - 1) == 'e') ||
                        !(i + 1 < s.length() && (s.charAt(i + 1)>= '0' && s.charAt(i + 1) <= '9')))
                    return false;
            }//+ 出现过e
            else if(!((ch >= '0' && ch <= '9') || ch == '.' || ch == 'e')){
                return false;
            }
        }
        
        return result;
    }
}

还是要先看一下哪一些是合理的，可以先百度一下。在实现，要不然后面要针对测试用例一个个修改，严重拉低通过率