請實現(xiàn)一個函數(shù)用來判斷字符串是否表示數(shù)值（包括整數(shù)和小數(shù)）。例如，字符串"+100","5e2","-123","3.1416"和"-1E-16"都表示數(shù)值。 但是"12e","1a3.14","1.2.3","+-5"和"12e+4.3"都不是。

直接遍歷判斷

public class Solution {    public boolean isNumeric(char[] str) {        boolean hasE = false ;         boolean hasDot = false ;         boolean hasNum = false ;         for(int i = 0;i < str.length;i++){            if(str[i] == '+'||str[i]=='-'){                if(i == 0)continue ;                if(str[i-1] == 'e'||str[i-1] == 'E')continue ;                 return false ;             }else if(str[i] == '.'){                if(hasE)return false ;                 if(hasDot)return false ;                 if(i!= 0 &&(str[i-1] < '0' || str[i-1] > '9')){                    if(str[i-1]!='+' && str[i-1]!='-')                        return false  ;                 }                 hasDot = true ;             }else if(str[i] == 'e' || str[i] == 'E'){                hasE = true ;             }else if(str[i] < '0' || str[i] > '9'){                return false ;             }else{                if(hasE)hasNum = true ;            }        }        if(hasE)return hasNum ;         return true ;     }}