LeetCode08 字符转成数字

image-20230302212427430

方法一：

引入自动状态机概念

自动状态机 有四种状态：

开始状态 -> 转换状态 -> 计算状态 -> 结束状态

image-20230302224008826

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class Solution{
 
    
 class Automaton {
 int sign = 1;
 long ans = 0;
 final String START ="start";
 final String SIGN ="signd";
 final String IN_NUMBER="in_number";
 final String END ="end";
 String state = START;
 
 private Map<String, String[]> map = new HashMap<>(){{
     put("start",new String[]{START,SIGN,IN_NUMBER,END});
     put("signd",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 getState(char c){
     if(c==' '){
         return 0;
     }
     if(c == '-'||c=='+'){
         return 1;
     }
     if(c >= '0' && c <= '9'){
         return 2;
     }
     return 3;
 }
     
 public void get(char c) {
  	state  = map.get(state)[getState(c)];
    if(IN_NUMBER.equals(state)){
       ans = ans * 10 + c - '0';
       if(sign == 1){
           ans =Math.min(ans,Integer.MAX_VALUE);
       }else{
           ans = Math.min(ans, -(long)Integer.MIN_VALUE);
       }
    }else if(SIGN.equals(state)){
        sign = c =='+'?1:-1;
    }
 }

 }
    
    
 public int myAtoi(String str) {
    Automaton an = new Automaton();
    char[]  charry =str.toCharArray();
 	for(char c : charry){
        an.get(c);
    }    
 	return an.sign * ((int)an.ans);
}




}










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