leetcoede 8 字符串转换整数

class At{
    string state="start";
    unordered_map<string,vector<string>>table={
        {"start",{"start","signed","in_number","end"}},
        {"in_number",{"end","end","in_number","end"}},
        {"signed",{"end","end","in_number","end"}},
        {"end",{"end","end","end","end"}}
    };//状态转换图
    int get_c(char c){
        if(c==' '){
            return 0;
        }else if(c=='+'||c=='-'){
            return 1;
        }else if(c>='0'&&c<='9'){
            return 2;
        }
        return 3;
    }//分别对应空格，加减，数字，其他
public:
    int sign=1;
    long long ans=0;
    void get(char c){
        state=table[state][get_c(c)];
        if(state=="signed"){
            sign=c=='+'? 1:-1;
        }else if(state=="in_number"){
            ans=ans*10+c-'0';
            ans=sign==1?min(ans,(long long)INT_MAX):min(ans,-(long long)INT_MIN);//注意点INT_MAX!=-INT_MIN
        }
    }
};
class Solution {
public:
    int myAtoi(string str) {
        At at;
        for(auto x:str){
            at.get(x);
        }
        return at.sign*at.ans;
    }
};