比较两个字符串，删除评论元素

可以不用循环
但是需要设置好所有的API

NSString *str1=@"0,1,2,3";
NSString *str2=@"1,2";

NSMutableArray *arr1=[[NSMutableArray alloc]initWithArray:[str1 componentsSeparatedByString:@","]];

[arr1 removeObjectsInArray:[str2 componentsSeparatedByString:@","]];
NSLog(@"arr1 %@",arr1);
/*
NSMutableString *finalString=[NSMutableString new];

for (NSInteger i=0; i<[arr1 count]; i++) {
    NSString *str=[arr1 objectAtIndex:i];

    [finalString appendString:str];
    if (i!=[arr1 count]-1) {
      [finalString appendString:@","];  
    }
}
*/
NSString *finalString=[arr1 componentsJoinedByString:@","];
NSLog(@"finalString %@",finalString);