Fractal Software Engineer interview questions

Interface,abstract class and difference between them,string concepts ,difference between string builder and string buffer Technical ques:- hello xyz1 abc Output:- abc xyz1 hello I am solving the question by taking each word in a matrix and then i got run time error so i tell them give me time to check my mistake but they told me i understand your logic so i said it will take few more minutes to solve and the error was array size should be 3 but i got 2 as you can see the space. But in feedback i got improve your logic from hr and i am confident if that person comes in coding round i will defeat him by half of his time.

What were your learning experience in previous organization?