20.12.30 leetcode8 自动机

题目链接：https://leetcode-cn.com/problems/string-to-integer-atoi/

题意：将字符串转换为整数

分析：有限状态自动机的题，以前好像没做过，直接看题解吧

class Solution {
    public int myAtoi(String s) {
        Automaton automaton = new Automaton();
        int len = s.length();
        for(int i=0;i<len;i++){
            automaton.get(s.charAt(i));
        }
        return (int)(automaton.sign*automaton.ans);
    }
}

class Automaton{
    public int sign = 1;
    public long ans = 0;
    private String state = "start";
    private Map<String,String[]> table = new HashMap<String,String[]>(){{
        put("start", new String[]{"start", "signed", "in_number", "end"});
        put("signed", new String[]{"end", "end", "in_number", "end"});
        put("in_number", new String[]{"end", "end", "in_number", "end"});
        put("end", new String[]{"end", "end", "end", "end"});
    }};

    private int get_col(char c){
        if(c==' ')return 0;
        if (c == '+' || c == '-') {
            return 1;
        }
        if (Character.isDigit(c)) {
            return 2;
        }
        return 3;
    }

    public void get(char c){
        state = table.get(state)[get_col(c)];
        if("in_number".equals(state)){
            ans = ans*10+c-'0';
            ans = sign == 1 ? Math.min(ans, (long) Integer.MAX_VALUE) : Math.min(ans, -(long) Integer.MIN_VALUE);
        }else if("signed".equals(state)){
            sign = c == '+' ?1:-1;
        }
    }
}