PTC Internship interview questions

Questions asked in a technical interview: 1) Introduce yourself 2) Then he asked me to explain my projects. My project was in the MERN stack, so he asked me to show my project, since I have hosted it, I directly showed that. Then he asked many cross questions like some react, redux concepts, how you have implemented error handling. How you have done routing with express. Where you have hosted your database, request-response, REST, REST vs GraphQL, different HTTP status codes. Since I have hosted on the Digital Ocean platform, he also asked how DNS, SSH works, which webserver you have used and why? Overall it was a good discussion and the interviewer had detailed knowledge of this domain 3) Then he asked which language you are comfortable in? I said C++ 4) Memory management in C++ 5) Generics in C++ 6) Have you ever used the STL library. I said yes, then he asked me to explain how does hashmap works internally. Which data structures does it use? 7) Diamond problem 8) Virtual functions, pure virtual functions, virtual destructor use case 9) Friend function use case 10) How does C++ compilation works. Different stages in the compilation 11) Then he asked me to write OOP style code for Linked list operations - a) Add node to a linked list, b)Delete n'th node from a linked list. I shared the screen and showed output with sample test case 12) At last, 2 puzzles

What is singleton in java.