题目：

参考解法：（DFA）

class Solution {
public:bool isNumber(string str) {int state=0, flag=0; // flag to judge the special case "."while(str[0]==' ')  str.erase(0,1);//delete the  prefix whitespace while(str[str.length()-1]==' ') str.erase(str.length()-1, 1);//delete the suffix whitespacefor(int i=0; i<str.length(); i++){if('0'<=str[i] && str[i]<='9'){flag=1;if(state<=2) state=2;else state=(state<=5)?5:7;}else if('+'==str[i] || '-'==str[i]){if(state==0 || state==3) state++;else return false;}else if('.'==str[i]){if(state<=2) state=6;else return false;}else if('e'==str[i]){if(flag&&(state==2 || state==6 || state==7)) state=3;else return false;}else return false;}return (state==2 || state==5 || (flag&&state==6) || state==7);}
};