LeetCode65——Valid Number（使用DFA）来判断字符串是否为数字

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 whitespace
for(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);
}
};