Implement atoi to convert a string to an integer.

Hint: Carefully consider all possible input cases. If you want a challenge, please do not see below and ask yourself what are the possible input cases.

Notes: It is intended for this problem to be specified vaguely (ie, no given input specs). You are responsible to gather all the input requirements up front.

程式碼

public class Solution {
    public int atoi(String str) {
  		String num_str="";
        char[] str_char=str.toCharArray();
        char[] sympo="-+".toCharArray();
        boolean abs=true;
        for(int i=0;i<str.length();i++){
        	 if(str_char[i]==sympo[0] ||str_char[i]==sympo[1]){
        		 if(!Character.isDigit(str_char[i+1])){
        			 return 0;
        		 }
        		 if(str_char[i]==sympo[0]){
        			 abs=false;
        		 }
        	 }
      	  if(Character.isDigit(str_char[i])){       		 
   	   	      num_str+=String.valueOf(str_char[i]);      	   	 
   	        }
      	  else{
      		  if(num_str.length()!=0){
      			  break;
      		  }
      	  }
//       	  if(Character.isDigit(str_char[i])){       		 
//       	   	 num_str+=String.valueOf(str_char[i]);      	   	 
//       	    }
       	 if(num_str!=""){
       	   if(Math.abs(Integer.parseInt(num_str))>=Integer.MAX_VALUE / 10){
  		      return Integer.MAX_VALUE;
  	          }
       	   }
       }
        if(num_str!=""){
        	 if(abs){
        		 return Integer.parseInt(num_str);
        		 }
        	 else{
        		 return -Integer.parseInt(num_str);
        	 }
	    }
        else{
        	   return 0;
        
  }
    
 }
    
}