8 字符串转换整数(atoi)

上面是官方自动机图解模型

#官方python代码
#
# @lc app=leetcode.cn id=8 lang=python3
#
# [8] 字符串转换整数 (atoi)
#

# @lc code=start
INT_MAX = 2**31-1
INT_MIN = -2**31


class Automaton:
    def __init__(self):
        self.state = 'start'
        self.sign = 1
        self.ans = 0
        self.table = {
            'start': ['start', 'signed', 'in_number', 'end'],
            'signed': ['end', 'end', 'in_number', 'end'],
            'in_number': ['end', 'end', 'in_number', 'end'],
            'end': ['end', 'end', 'end', 'end'],
        }

    def get_col(self, c):
        if c.isspace():  # 查看字符是否为空白
            return 0
        if c == '+' or c == '-':
            return 1
        if c.isdigit():
            return 2
        return 3

    def get(self, c):
        self.state = self.table[self.state][self.get_col(c)]
        if self.state == 'in_number':
            self.ans = self.ans*10+int(c)
            self.ans = min(self.ans, INT_MAX) if self.sign == 1 else min(
                self.ans, -INT_MIN)
        elif self.state == 'signed':
            self.sign = 1 if c == '+' else -1


class Solution:
    def myAtoi(self, s: str) -> int:
        automaton = Automaton()
        for c in s:
            automaton.get(c)
        return automaton.sign*automaton.ans


# @lc code=end

//官方C++代码
class Automation{
    string state="start";
    unordered_map<string,vector<string>> tabel={
        {"start",{"start","signed","in_number","end"}},
        {"signed",{"end","end","in_number","end"}},
        {"in_number",{"end","end","in_number","end"}},
        {"end",{"end","end","end","end"}}
    };
    int get_col(char c){
        if(isspace(c)) return 0;
        if(c=='+' or c=='-') return 1;
        if(isdigit(c)) return 2;
        return 3;
    }
public:
    int sign=1;
    long long ans=0;
    void get(char c){
        state=tabel[state][get_col(c)];
        if (state=="in_number"){
            ans=ans*10+c-'0';
            ans=sign==1?min(ans,(long long)INT_MAX):min(ans,-(long long)INT_MIN);
        }
        else if(state=="signed")
        sign=c=='+'?1:-1;
    }
};

class Solution {
public:
    int myAtoi(string s) {
        Automation automation;
        for (char c:s)
            automation.get(c);
        return automation.sign * automation.ans;

    }
};